Wheel alignment measuring instrument and wheel alignment measuring

ABSTRACT

A wheel alignment method and device that includes an image pick-up unit that picks up an image of the measuring surface of a measuring plate so that at least a part of measuring marks drawn on the measuring plate are included in the picked-up image. A judging unit judges which measuring mark is included in the image picked up by the image pick-up unit. Based upon the relationship between the selected measuring mark and a measuring object position in the image picked up by the image pick-up unit, the position on the measuring plate corresponding to the measuring object position is calculated, thereby quickly determining the position of the measuring plate corresponding to the measuring object in a non-contact manner.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wheel alignment measuring device andwheel alignment measuring method for measuring wheel alignment tothree-dimensionally detect displacement and inclination of a wheel of adriven vehicle with a vehicle basic characteristics detecting device.

2. Related Art

A vehicle basic characteristics detecting device is known as a testdevice for measuring the basic characteristics of a vehicle, such assuspension characteristics or steering characteristics, in a testchamber.

In such a vehicle basic characteristics detecting device, the vehicle tobe measured is fixed in a predetermined position, and rotational force,horizontal force, and vertical force are applied to the wheels. Byprocessing the measurement data obtained from the reaction force, thebasic characteristics can be detected.

As a part of the vehicle basic characteristics detecting device, thereis a wheel alignment measuring device for measuring wheel alignment,such as spin angle, camber angle, and toe angle, based on the distancefrom a reference position to the side surface of the wheel.

A conventional wheel alignment measuring device is fixed onto a platformwhich supports the wheel and is driven by an actuator. Being connectedto the wheel, it generally detects movement of the wheel. The problemwith this type of mechanical wheel alignment measuring device is thatmeasurements cannot be made at high speed because of a decrease inmeasuring accuracy caused by friction of the moving parts andrestrictions due to the inertial mass of the components or the like.

First Embodiment of the Prior Art

To solve the problem, a non-contact type wheel alignment measuringdevice provided with a non-contact type distance sensors such as laserbeam sensors and ultrasonic sensors.

More specifically, a conventional optical wheel alignment measuringdevice comprises a measuring unit provided with a plurality of opticalsensors (laser displacement gauges, for instance). This measuring unitis disposed on the platform on the side of a wheel. The distance from apredetermined reference position to the measuring plate attached to theside surface of the wheel is optically measured by moving the measuringunit in the longitudinal direction of the vehicle. Based on the obtainedmeasurement data, the camber angle and toe angle are determined.

In the optical wheel alignment measuring device of the first example,the measuring plate is attached to the wheel with a jig which isprovided to the wheel beforehand. An adjuster of the attachment jigadjusts the center of the attachment jig to the center of the wheel. Afitting provided to the measuring plate for restricting the attachmentposition is then connected to the attachment jig by a magnet provided tothe attachment jig.

With the wheel alignment measuring device of the first example, theposition of the measuring plate needs to be adjusted by the adjuster ofthe attachment jig, which is time-consuming.

Due to the attachment jig, the distance from the center of the width ofthe wheel to the measuring surface of the target plate becomes longer,i.e., the radius of the rotational axis of the measuring surface becomeslarger. So, if the wheel inclines at a large angle, or if the camberangle greatly varies during the measurement, the amount of movement ofthe measuring surface becomes large. This results in a problem that thearea of the limited measuring surface cannot be effectively utilized.

Also, the laser displacement gauges of the first example of the priorart are driven in a two-dimensional stage based on the origin of themeasuring plate, so that the laser displacement gauges follow themovement of the measuring plate, and that the laser beam is alwaysemitted onto the measuring plate.

As a result, the structure of the device becomes complicated, and themanufacturing cost becomes high.

Also, the two-dimensional driving control operation for driving thelaser displacement gauges becomes complicated, so does the adjustmentoperation of the laser displacement gauges for improving the measuringaccuracy.

Second Embodiment of the Prior Art

In an optical wheel alignment measuring device of the second example ofthe prior art, three laser displacement gauges are employed formeasuring the camber angle and toe angle. Two of the laser displacementgauges are a first laser displacement gauge and a second laserdisplacement gauge. The first laser displacement gauge irradiatesmeasuring light onto a position at a first predetermined distance fromthe rotational center of the wheel in a first horizontal direction onthe measuring plate. The second laser displacement gauge irradiates themeasuring light onto a position at a second predetermined distance inthe vertical direction. The remaining third laser displacement gaugeirradiates the measuring light onto a position at a third predetermineddistance from the rotational center in a second horizontal directionopposite from the first horizontal direction. The position irradiated bythe third laser displacement gauge is situated on a line perpendicularto the vertical line extending through the rotational center.

In such a case, the camber angle is calculated from the displacementdifference between the distance from the measuring plate measured by thefirst laser displacement gauge and the distance from the measuring platemeasured by the second laser displacement gauge, and the distance LZ′between the laser beam irradiation point of the first laser displacementgauge and the laser beam irradiation point of the second laserdisplacement gauge.

More specifically, the camber angle θCAM can be calculated by thefollowing formula:

θCAM=tan⁻¹(|L 1−L 2|)/LZ′

where the distance from the measuring plate measured by the first laserdisplacement gauge is L1, and the distance from the measuring platemeasured by the second laser displacement gauge is L2.

The toe angle is calculated from the displacement difference between thedistance from the measuring plate measured by the third laserdisplacement gauge and the distance from the measuring plate measured bythe first (or second) laser displacement gauge, and the distance LXbetween the laser beam irradiation point of the third laser displacementgauge and a line in parallel with the Z-direction (vertical direction)including the laser beam irradiation point on a plane containing thelaser beam irradiation point of the first (or second) laser displacementgauge.

More specifically, the camber angle θCAM can be calculated by thefollowing formula:

θCAM=tan⁻¹(|L 3−L 1|)/LX

where the distance from the measuring plate measured by the third laserdisplacement gauge is L3, and the distance from the measuring platemeasured by the first laser displacement gauge is L1.

In this case, even if the amount of movement in the Z direction islarge, the distance LZ′ between the first laser displacement gauge andthe second laser displacement gauge cannot be made long.

This is because the laser beam emitted from all the laser displacementgauges is required to irradiate the measuring plate in the camber angleand toe angle measurement, in both cases where the measuring plate issituated in the highest possible position in the Z direction and wherethe measuring plate is situated in the lowest possible position in the Zdirection.

In other words, the laser beam irradiation points of all the laserdisplacement gauges should exist within an area surrounded by thehighest possible position and the lowest possible position that themeasuring light from the laser displacement gauges can be emitted ontothe measuring plate.

As a result, the measuring accuracy of the camber angle θCAM cannot beensured.

On the other hand, if the measuring accuracy of the camber angle θCAM isincreased, the distance LZ′ between the laser beam irradiation point ofthe first laser displacement gauge and the laser beam irradiation pointof the second displacement gauge needs to be long. As a result, themeasurable range, which is the difference between the highest possibleposition and the lowest possible position, cannot be made wide.

Third Embodiment of the Prior Art

A ultrasonic wheel alignment measuring device of the third embodiment ofthe prior art is provided with a plurality of ultrasonic sensors inpredetermined positions on the side of the wheel. The ultrasonic sensorsmeasure the distance from a predetermined reference position to themeasuring plate attached to the side surface of the wheel. Based on theobtained measurement data, the camber angle and toe angle aredetermined. Japanese Utility Model Laid-Open No. 63-44107 discloses moredetails.

Fourth Embodiment of the Prior Art

An optical wheel alignment measuring device of the fourth embodiment ofthe prior art is provided, on a platform on the side of a wheel, with ameasuring unit comprising a plurality of optical sensors (laserdisplacement gauges, for instance). The measuring unit moves in thelongitudinal direction of the vehicle so as to optically measure thedistance from a predetermined reference position to the measuring plateattached to the side surface of the wheel. Based on the obtainedmeasurement data, the camber angle and toe angle are determined.Japanese Patent Laid-Open No. 63-94103 discloses more details.

The ultrasonic wheel alignment measuring device of the third embodimentof the prior art is capable of measuring a large amount of displacement,but the allowable range of the inclination of the sensor axis of eachultrasonic sensor is ±7° from the limit of the reflection angle. Also,the ultrasonic wheel alignment measuring device cannot be used in wheelalignment measurement whose inclination range is wide.

In the case of the optical wheel alignment measuring device with thelaser displacement gauges of the fourth embodiment of the prior art, itis difficult to have a measurable displacement range (measurabledistance range) of ±100 mm, with a reference distance set between themeasuring surface of the measuring plate and the laser displacementgauges. Setting such a measuring displacement range will result in lowaccuracy and high cost. For this reason, an optical wheel alignmentmeasuring device in practical use is fixed onto a platform, so thatlaser displacement gauges of small measurable displacement range can beused in measurement.

In such a case, the wheel alignment to be actually measured is thealignment with respect to the vehicle body.

With the vehicle body being fixed onto a predetermined referenceposition, even if the platform is displaced with respect to thereference position by starting the actuator, the relative positionalrelationship between the platform and the wheel alignment measuringdevice will not change, and the wheel alignment measurement data shouldinclude the amount of displacement of the platform.

However, the amount of displacement of the platform contains errorscaused by rigid deformation of the platform, and such errors cannot beexcluded from the measurement data. This results in inaccurate wheelalignment measurement, with the measurement data containing measurementerrors.

To exclude the measurement errors, data correction can be performed.However, error causing conditions greatly vary, and appropriatecorrection cannot always be performed, which results in poor measuringaccuracy, reliability, and reproducibility.

Since the amount of platform displacement cannot be excluded from themeasurement data, the measurement data end up including measurementerrors, which hinders accurate wheel alignment measurement.

To exclude the measurement errors, data correction can be performed.However, measuring conditions greatly vary, and appropriate correctioncannot always be performed, which results in poor measuring accuracy,reliability, and reproducibility.

SUMMARY OF THE INVENTION

To solve the above problems, a first object of the present invention isto provide a wheel alignment measuring device and a wheel alignmentmeasuring method which can make a wheel alignment measurement with asimpler structure at a lower manufacturing cost. By this device andmethod, the adjustment of the measuring plate becomes simpler, and therotational radius of the measuring surface is minimized so that the areaof the measuring surface can be effectively utilized.

A second object of the present invention is to provide a wheel alignmentmeasuring device and a wheel alignment measuring method with a simplerstructure at a lower manufacturing cost. By this device and method,control and adjustment operations become easier.

A third object of the present invention is to provide a wheel alignmentmeasuring device and a wheel alignment measuring method with a simplerstructure and a simpler control procedure. By this device and method,wheel alignment measurements can be taken at high speed, and themeasuring accuracy of the camber angle θCAM is maintained.

A fourth object of the present invention is to provide a caster anglemeasuring device, a wheel alignment measuring device, a caster anglemeasuring method, and a wheel alignment measuring method. By thesedevices and methods, a non-contact caster angle can be measured with adesired accuracy.

A fifth object of the present invention is to provide a measuring plate,a wheel alignment measuring device, and a wheel alignment measuringmethod, by which the positional relationship between the measuring plateand the wheel alignment measuring device can be constantly and quicklydetected. Thus, accuracy, reliability, and reproducibility in wheelalignment measurement can be improved.

A sixth object of the present invention is to provide a measuring plate,a wheel alignment measuring device, and a wheel alignment measuringmethod, by which the positional relationship between the measuring plateand the wheel alignment measuring device can be surely and quicklydetected. Thus, accuracy, reliability, and reproducibility in alignmentmeasurement can be improved.

To achieve the first object, the present invention provides a wheelalignment measuring device which measures wheel alignment using ameasuring plate provided with a rotational center specifying mark on themeasuring surface thereof and attached to a wheel of a vehicle beingmeasured. This wheel alignment measuring device comprises: a casterangle detecting unit for detecting a caster angle of the measuringplate; a mark coordinate detecting unit for detecting mark coordinateswhich are the coordinates in an absolute space of the rotational centerspecifying mark; and a rotational center coordinate calculating unit forcalculating current rotational center coordinates which are thecoordinates of a current rotational center of the measuring surface ofthe measuring plate in the absolute space.

According to this embodiment, the rotational center coordinatecalculating unit calculates the current rotational center coordinates inthe absolute space of the measuring surface of the measuring plate basedon the caster angle detected by the caster angle detecting unit and themark coordinates detected by the mark coordinate detecting unit. Thus,accurate wheel alignment measurements can be taken by detecting therotational center position of the wheel, without attaching the measuringplate in line with the rotational center in advance.

Also, there is no need to provide the measuring plate with a jig foradjusting the rotational center position. This reduces the thickness ofthe measuring plate in the transverse direction of the vehicle beingmeasured. Thus, the rotational radius of the wheel at the time of a toeangle change can be made smaller, so that the area of the measuringsurface of the measuring plate can be effectively utilized.

In a preferred embodiment of the present invention the rotational centercoordinate calculating unit comprises: a real mark coordinatecalculating unit for calculating reference mark coordinates which arecurrent initial mark coordinates corresponding to the coordinates of therotational center specifying mark with the origin being initialrotational coordinates corresponding to the initial values of therotational center coordinates, based on the caster angle and the markcoordinates; and a current center coordinate calculating unit forcalculating the current rotational center coordinates based on thereference mark coordinates.

According to this embodiment, the real mark coordinate calculating unitof the rotational center coordinate calculating unit calculates thereference mark coordinates, which are the current coordinates of theinitial mark coordinates that are the coordinates of the rotationalcenter specifying mark predetermined as the origin, and the currentcenter coordinate calculating unit calculate the current rotationalcenter coordinates based on the reference mark coordinates determined bythe real mark coordinate calculating unit. Thus, the rotational centerposition of the wheel can be calculated from only a small amount ofdata.

In a preferred embodiment of the present invention the real markcoordinate calculating unit calculates the reference mark coordinatesusing formulas (1) and (2):

X 0″=X 0′ cos(θCAS)+Z 0′ sin(θCAS)  (1)

Z 0″=−X 0′ sin(θCAS)+Z 0′ cos(θCAS)  (2)

and the current center coordinate calculating unit calculates thecurrent rotational center coordinates (X0, Z0) using formulas (3) and(4):

X 0=X 0′−X 00+XX  (3)

Z 0=Z 0″−Z 00+ZZ  (4)

where the caster angle measured counterclockwise is θCAS, the markcoordinates are (X0′, Z0′), the reference mark coordinates are (X0″,Z0″), the initial mark coordinates are (X00, Z00), and the initialrotational center coordinates are (XX, ZZ).

According to this embodiment, the real mark coordinate calculating unitcalculates the reference mark coordinates using the formulas (1) and(2), and the current center coordinate calculating unit calculates thecurrent rotational center coordinates (X0, Z0) using the formulas (3)and (4). Thus, the rotational center position can be given by simpleformulas, and real time processing can be performed without complicatingthe control operation of the arithmetic operation unit.

In a preferred embodiment of the present invention measuring wheelalignment is performed using a measuring plate provided with arotational center specifying mark on its measuring surface and attachedto a wheel of a vehicle being measured. This method comprises: a casterangle detecting step of detecting the caster angle of the measuringplate; a mark coordinate detecting step of detecting mark coordinateswhich are the coordinates of the rotational center specifying mark in anabsolute space; and a rotational center coordinate calculating step ofcalculating current rotational center coordinates which are therotational center coordinates of the measuring surface of the measuringplate in the absolute space at present, based on the detected casterangle and the mark coordinates.

According to this embodiment, in the rotational center coordinatecalculating step, the current rotational center coordinates that are therotational center coordinates of the measuring surface of the measuringplate in the absolute space at present is calculated based on the casterangle detected in the caster angle detecting step and the markcoordinates detected in the mark coordinate detecting step. Thus, therotational center position of the wheel can be detected real timewithout adjusting the rotational center of the measuring platebeforehand, and accurate wheel alignment measurements can be taken.

Also, there is no need to provide the measuring plate with a jig foradjusting the rotational center. This reduces the thickness of themeasuring plate in the transverse direction of the vehicle beingmeasured. Thus, the rotational radius at the time of a two angle changeof the wheel can be reduced, and the area of the measuring surface ofthe measuring plate can be effectively utilized.

In a preferred embodiment of the present invention the rotational centercoordinate calculating step comprises: a real mark coordinatecalculating step of calculating reference mark coordinates which are thecurrent coordinates of an initial mark coordinate, i.e., the coordinatesof the rotational center specifying mark predetermined with the originbeing initial rotational center coordinates corresponding to the initialvalues of the rotational center coordinates, based on the caster angleand the mark coordinates; and a current center coordinate calculatingstep of calculating the current rotational center coordinates.

According to this embodiment, in the real mark coordinate calculatingstep, the reference mark coordinates that are the current coordinates ofthe initial mark coordinates as the coordinates of the rotational centerspecifying mark predetermined with the origin being the initialrotational center coordinates, which are the initial value of therotational center coordinates, are calculated based on the caster angleand the mark coordinates. In the current center coordinate calculatingstep, the current rotational center coordinates are calculated based onthe reference mark coordinates obtained in the real mark coordinatecalculating step. Thus, the rotational center position of the wheel canbe quickly calculated from only a small amount of data.

In a preferred embodiment of the present invention the reference markcoordinates are calculated in the real mark coordinate calculating stepusing formulas (1) and (2):

X 0″=X 0′ cos(θCAS)+Z 0′ sin(θCAS)  (1)

Z 0″=−X 0′ sin(θCAS)+Z 0′ cos(θCAS)  (2)

and the current rotational center coordinates (X0, Z0) are calculated inthe current center coordinate calculating step using formulas (3) and(4):

X 0=X 0′−X 00+XX  (3)

Z 0=Z 0″−Z 00+ZZ  (4)

where the caster angle measured counterclockwise is θCAS, the markcoordinates are (X0′, Z0′), the reference mark coordinates are (X0″,Z0″), the initial mark coordinates are (X00, Z00), and the initialrotational center coordinates are (XX, ZZ).

According to this embodiment, the reference mark coordinates arecalculated using the formulas (1) and (2) in the real mark coordinatecalculating step, and the current center coordinates (X0, Z0) arecalculated using the formulas (3) and (4) in the current centercoordinate calculating step . Thus, the rotational center position canbe calculated by simple arithmetic operations, and real time processingcan be performed without complicating the control operation by thearithmetic operation unit.

To achieve the second object, the present invention provides a measuringplate attached to a wheel of a vehicle being measured so that the origincorresponds to the rotational center of the wheel. This measuring platecomprises: a measuring mark area which formed in an area surrounding andcontaining the origin, and provided with various types of measuringmarks; and a distance measuring area which is optically uniform andexposed to distance measuring light from the outside, and extends in thelongitudinal direction of the vehicle being measured.

According to this embodiment, the measuring plate is provided with theoptically uniform distance measuring area in the longitudinal directionof the vehicle being measured. Thus, by emitting the distance measuringlight onto the distance measuring area, the distance from the measuringplate can be accurately measured, thereby improving the accuracy inwheel alignment measurement.

Since the distance measuring area can be large, an external distancemeasuring light emitting unit can be used on a fixed state. Thus, thestructure of the wheel alignment measuring device can be simplifiedwithout reducing the measuring accuracy.

In a preferred embodiment of the present invention the distancemeasuring area extends in the longitudinal direction of the wheel of thevehicle being measured.

According to this embodiment, as the distance measuring area is formedin the longitudinal direction of the wheel of the vehicle beingmeasured, two rays of the distance measuring light can be emitted ontotwo positions further apart in the longitudinal direction of the wheel.Thus, the angle measurement of the measuring plate can be made with highprecision by calculating the difference between the lengths from theirradiation points of the two rays of the distance measuring light, andthe accuracy in wheel alignment measurement can be further improved.

In a preferred embodiment of the present invention the measuring markarea contains: a first reference mark whose center coordinates are theorigin of the measuring plate; a plurality of second reference markswhose center coordinates are at the intersections of first virtual linesand second virtual lines, the first virtual lines being in parallel witheach other, and the second virtual lines being in parallel with eachother and perpendicular to the first virtual lines; and a plurality ofcorrection lines which are in parallel with either the first virtuallines or the second virtual lines, and are situated at fixed intervals.

According to this embodiment, since the first reference mark, the secondreference marks, and the correction lines are drawn in the distancemeasuring mark area. Thus, various types of wheel alignment measurementscan be taken speedily and accurately by picking up an image of thedistance measuring mark area and performing image processing.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device comprises: at least two distance measuring units whichare fixed in predetermined reference positions at a predetermineddistance from each other, and emit the distance measuring light tooutput distance measuring signals corresponding to the distances fromthe measuring plate; and a distance calculating unit for calculating thedistance from a predetermined position on the measuring platecorresponding to a predetermined reference position, based on thedistance measuring signals.

According to this embodiment, the distance measuring units are fixed inthe predetermined reference positions, emit the distance measuringlight, and output the distance measuring signals corresponding to thedistances from the measuring plate. The distance calculating unitcalculates the distance from the predetermined position on the measuringplate corresponding to the reference position based on the distancemeasuring signals. In this embodiment, there is no need to employ adriving mechanism for driving the distance calculating unit, whichsimplifies the structure of the wheel alignment measuring device. Thus,the distance measuring accuracy, as well as the measuring plate anglemeasuring accuracy, can be maintained high.

To achieve the third object, the present invention provides a wheelalignment measuring device for measuring the distance from and theinclination of the measuring surface of a measuring plate which isattached to a wheel of a vehicle being measured so that the originthereof corresponds to the center of the rotational axis of the wheel.This wheel alignment measuring device comprises four or more (number N)distance measuring light emitting and receiving units which emitdistance measuring light onto the measuring surface, receive thedistance measuring light reflected by the measuring surface, and outputdistance measuring signals. Emitters of the distance measuring light arearranged on the same virtual plate at fixed intervals, so that thedistance measuring light of at least three of the N distance measuringlight emitting and receiving units can be emitted onto the measuringsurface under predetermined measuring conditions.

According to this embodiment, the distance measuring light is emittedonto the measuring surface by at least three distance measuring lightemitting and receiving units under the predetermined measuringconditions, and the N distance measuring light emitting and receivingunits receive the distance measuring light reflected by the distancemeasuring surface, thereby outputting the distance measuring signals. Inthis embodiment, measurements can be taken, with the distance measuringlight emitting and receiving units being fixed, and there is no need toemploy with a driving mechanism for driving the distance measuring lightemitting and receiving units. Thus, the structure and the controloperation can be simplified, and the device manufacturing cost can bereduced accordingly.

In a preferred embodiment of the present invention the virtual planecontains a straight line substantially in parallel with the verticaldirection of the vehicle being measured, and a virtual parallelogram isarranged on the virtual plane so that the straight line includes one ofthe diagonal lines of the virtual parallelogram. The emitters of four ofthe distance measuring light emitting and receiving units are arrangedat the comers of the virtual parallelogram, and the virtualparallelogram is arranged so that the distance measuring light isemitted from the emitters on the diagonal line not included in thestraight line within the common area between a first measuring surfacecorresponding to the measuring surface moved the longest possibledistance in a first direction along the straight line, and a secondmeasuring surface corresponding to the measuring surface moved thelongest possible distance in a second direction opposite from the firstdirection.

According to this embodiment, the distance measuring light is emitted onthe measuring surface by at least three distance measuring lightemitting units, which include one of the distance measuring lightemitting unit on the diagonal line included in the straight line and thetwo distance measuring light emitting units on the other diagonal line.With the three distance measuring light emitters, accurate wheelalignment measurements can be constantly taken.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises: a choosing unit for choosing thedistance measuring signal of the distance measuring light emitting andreceiving unit corresponding to the emitter, which emits the distancemeasuring light upon the measuring surface, between the two emitters onthe diagonal line included in the straight line; and a camber anglecalculating unit for calculating the camber angle of the measuringsurface based on the distance measuring signal chosen by the choosingunit, and distance measuring signals of the distance measuring lightemitting and receiving units corresponding to the two emitters on thediagonal line not included in the straight line.

According to this embodiment, the choosing unit chooses the distancemeasuring signal of a distance measuring light emitting and receivingunit corresponding to the emitter, which emits the distance measuringlight upon the measuring surface, between the two emitters on thediagonal line included in the straight line. The camber anglecalculating unit calculates the camber angle of the measuring surfacebased on the distance measuring signal chosen by the choosing unit andthe distance measuring signals of the distance measuring light emittingand receiving units corresponding to the emitters on the other diagonalline not included in the straight line. Thus, the camber angle can beaccurately calculated along with displacement of the measuring plate,without a driving mechanism for driving the distance measuring lightemitting and receiving units. Also, the distance between the distancemeasuring light emitting and receiving units included in the straightline and the other distance measuring light emitting and receiving unitsnot included in the straight line can be made longer, thereby improvingthe accuracy of the camber angle measurement.

The camber angle calculating unit calculates the camber angle of themeasuring surface based on the distance measuring signal chosen by thechoosing unit and the distance measuring signals of the distancemeasuring light emitting and receiving units corresponding to the twoemitters on the other diagonal line not included in the straight line.

In a preferred embodiment of the present invention the choosing unitcomprises a judging unit for judging whether the intersection of the twodiagonal lines is situated in the first direction or in the seconddirection with respect to the origin of the measuring surface, therebychoosing the corresponding distance measuring light emitting andreceiving unit.

According to this embodiment, the judging unit of the choosing unitjudges whether the intersection of the two diagonal lines is situated inthe first direction or in the second direction with respect to theorigin of the measuring surface, thereby choosing the correspondingdistance measuring light emitting and receiving unit. Thus, the distancemeasuring light emitting and receiving unit to be used in the camberangle calculation can be quickly selected, and the camber angle can becalculated speedily and accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprising: a distance measuring light emitting andreceiving step in which at least three rays of distance measuring lightamong N (N=4 or larger) rays of distance measuring light are emittedonto the measuring surface at predetermined intervals; and a camberangle calculating step of calculating the camber angle of the measuringsurface based on the received distance measuring light.

According to this embodiment, in the distance measuring light emittingand receiving step, at least three rays of distance measuring lightamong N (N=4 or larger) rays of distance measuring light are emittedonto the measuring surface at predetermined intervals. In the camberangle calculating step, the camber angle of the measuring surface iscalculated based on the receiving distance measuring light. Since nodriving control needs to be performed to conform to the displacement ofthe measuring surface, the control procedure can be simplified, and thecost for control system development can be lowered.

In a preferred embodiment of the present invention a virtual planecontains a straight line substantially in parallel with the verticaldirection of the vehicle being measured. Also, a virtual parallelogramis arranged on the virtual plane so that the straight line contains oneof the diagonal lines of the virtual parallelogram, and the distancemeasuring light is emitted from each corner of the virtual parallelogramand the distance measuring light reflected by the measuring surface isreceived in the distance measuring light emitting and receiving step.The distance measuring light emitted from two corners on the diagonalline not included in the straight line and from one of the comers on thediagonal line included in the straight line is received in the commonarea between a first measuring surface corresponding to the measuringsurface moved the longest possible distance in a first direction alongthe straight line, and a second measuring surface corresponding to themeasuring surface moved the longest possible distance in a seconddirection opposite from the first direction, thereby calculating thecamber angle in the camber angle calculating step.

According to this embodiment, in the distance measuring light emittingand receiving step, the distance measuring light is emitted from eachcomer of the virtual parallelogram, and the distance measuring lightreflected by the measuring surface is received. In the camber anglecalculating step, the camber angle is calculated based on the receiveddistance measuring light emitted from the two comers on the diagonalline not included in the straight lint included in the common areabetween the first measuring surface and the second measuring surface,and the received distance measuring light emitted from one of the comerson the other diagonal line. Thus, the camber angle can be accuratelycalculated in accordance with displacement of the measuring surface.

In a preferred embodiment of the present invention the camber anglecalculating step comprises: a choosing step of choosing a ray ofdistance measuring light irradiating the measuring surface between thetwo rays of distance measuring light emitted from the corners includedin the straight line; and a camber angle operation step of calculatingthe camber angle of the measuring surface based on the distancemeasuring light chosen in the choosing step and the two rays of distancemeasuring light emitted from the comers not included in the straightline.

According to this embodiment, in the choosing step, a ray of distancemeasuring light irradiating the measuring surface is chosen between thetwo rays of distance measuring light emitted from the comers included inthe straight line. In the camber angle operation step, the camber angleof the measuring surface is calculated based on the distance measuringlight chosen in the choosing step and the two rays of distance measuringlight emitted from the comers not included in the straight line. In thisembodiment, the camber angle can be accurately calculated in accordancewith displacement of the measuring plate, and the length of themeasuring light emitted from the two comers not included in the straightline can be made longer with respect to the distance measuring lightemitted from one of the comers included in the straight line. Thus, theaccuracy in the camber angle calculation can be improved.

In a preferred embodiment of the present invention the choosing stepcomprises a judging step of judging whether the intersection of the twodiagonal lines is situated in the first direction or in the seconddirection with respect to the origin of the measuring surface, therebychoosing the corresponding distance measuring light.

According to this embodiment, in the judging step, the distancemeasuring light is chosen by judging whether the intersection of the twodiagonal lines is situated in the first direction or in the seconddirection with respect to the origin of the measuring surface. Thus, thedistance measuring light can be chosen quickly, and the camber angle canbe calculated speedily and accurately.

To achieve the fourth object, the present invention provides a casterangle measuring device for outputting effective caster angle data θECAShaving a desired measuring accuracy based on image data obtained throughimage pick-up, by an external CCD camera, of a caster angle measuringobject line drawn on a wheel alignment measuring target plate providedto a vehicle. This caster angle measuring device comprises: an originalcaster angle data calculating unit for calculating original caster angledata θCAS by quantizing the caster angle formed by the measuring objectline with respect to a predetermined reference line based on the imagedata; and an effective data output unit for outputting the originalcaster angle data θCAS as the effective caster angle data θECAS when theoriginal caster angle data θCAS change in value.

According to this embodiment, the original caster angle data calculatingunit calculates the original caster angle data θCAS by quantizing thecaster angle formed by the measuring object line with respect to thepredetermined reference line based on the image data outputted by theexternal CCD camera. The effective data output unit outputs the originalcaster angle data θCAS as the effective caster angle data θECAS when theoriginal caster angle data θCAS change in value. Although the casterangle is optically calculated in a non-contact manner using the imagedata outputted by the CCD camera, the measuring accuracy in measuringthe caster angle can be maintained at a desired level. Thus, with theeffective caster angle data θECAS, the wheel alignment can be quicklymeasured with a desired accuracy.

In a preferred embodiment of the present invention a caster anglemeasuring device is provided for outputting effective caster angle dataθECAS having a desired measuring accuracy based on image data obtainedthrough image pick-up, by an external CCD camera, of a caster anglemeasuring object line drawn on a wheel alignment measuring target plateprovided to a vehicle. This caster angle measuring device comprises: anoriginal caster angle data calculating unit for calculating originalcaster angle data θCAS based on the image data when the caster angleformed by the measuring object line with respect to a predeterminedreference line constantly increases or decreases; a comparator comparingoriginal caster angle data θCAS(n−1) in the previous measurement withoriginal caster angle data θCAS(n) in the current measurement; and aneffective data output unit for outputting the original caster angle dataθCAS(n) of the current measurement as the effective caster angle dataθECAS when the previous original caster angle data θCAS(n−1) is notequal to the current original caster angle data θCAS(n) as a result ofthe comparison.

According to this embodiment, the original caster angle data calculatingunit calculates the original caster angle data θCAS based on the imagedata when the caster angle formed by the measuring object line withrespect to the predetermined reference line constantly increases ordecreases. The comparator compares the original caster angle dataθCAS(n−1) in the previous measurement with the original caster angledata θCAS(n) in the current measurement. The effective data output unitoutputs the original caster angle data θCAS(n) of the currentmeasurement as the effective caster angle data θECAS when the previousoriginal caster angle data θCAS(n−1) is not equal to the currentoriginal caster angle data θCAS(n) as a result of the comparison.Although the caster angle is calculated in a non-contact manner usingthe image data outputted by the CCD camera, the measuring accuracy inmeasuring the caster angle can be maintained at a desired level. Thus,with the effective caster angle data θECAS, the wheel alignment can bequickly measured with a desired accuracy.

In a preferred embodiment of the present invention the original casterangle data calculating unit comprises: a line extracting unit forextracting the measuring object line based on the image data; and aninclination calculating unit for calculating the inclination of theextracted measuring object line by the method of least squares.

According to this embodiment, the line extracting unit extracts themeasuring object line based on the image data, and the inclinationcalculating unit calculates the inclination of the extracted measuringobject line by the method of least squares. Thus, the effective casterangle data θECAS can be calculated speedily and accurately.

In a preferred embodiment of the present invention the original casterangle data calculating unit comprises: a line extracting unit forextracting the measuring object line based on the image data; and aninclination calculating unit for calculating the inclination of theextracted measuring object line by the method of least squares.

According to this embodiment, the line extracting unit extracts themeasuring object line based on the image data, and the inclinationcalculating unit calculates the inclination of the extracted measuringobject line by the method of least squares. Thus, the effective casterangle data θECAS can be calculated speedily and accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device comprises: a CCD camera for outputting image data bypicking up an image of a caster angle measuring object line drawn on awheel alignment measuring target plate attached to a vehicle; the casterangle measuring device; and a data comparing unit for comparing theeffective caster angle data θECAS with measuring data of anotherdimension measured at substantially the same time that a change occursto the original caster angle data θCAS.

According to this embodiment, the CCD camera picks up an image of thecaster angle measuring object line drawn on the wheel alignmentmeasuring target plate attached to the vehicle, and outputs the imagedata to the caster angle measuring device. The caster angle measuringdevice outputs the effective caster angle data θECAS to the datacomparing unit. The data comparing unit compares the effective casterangle data θECAS with measuring data of another dimension measured atsubstantially the same time that a change occurs to the original casterangle data θCAS. Thus, various data in wheel alignment measurement canbe compared with the caster angle data with a desired accuracy.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device comprises: a CCD camera for outputting image data bypicking up an image of a caster angle measuring object line drawn on awheel alignment measuring target plate attached to a vehicle; the casterangle measuring device; and a data comparing unit for comparing thecurrent original caster angle data θCAS(n) with measuring data ofanother dimension measured at substantially the same time as themeasurement of the current original caster angle data θCAS(n).

According to this embodiment, the CCD camera picks up an image of thecaster angle measuring object line drawn on the wheel alignmentmeasuring target plate attached to the vehicle, and outputs the imagedata to the caster angle measuring device. The caster angle measuringdevice outputs the current original caster angle data θCAS(n) as theeffective caster angle data θECAS to the data comparing unit. The datacomparing unit compares the current original caster angle data θCAS(n)with measuring data of another dimension measured at substantially thesame time as the measurement of the current original caster angle dataθCAS(n). Thus, various data in wheel alignment measurement can becompared with the caster angle data with a desired accuracy.

In a preferred embodiment of the present invention the caster anglemeasuring method for calculating an effective caster angle θECAS havinga desired measuring accuracy based on image data is obtained throughimage pick-up, by an external CCD camera, of a caster angle measuringobject line drawn on a wheel alignment measuring target plate attachedto a vehicle. This caster angle measuring method comprises: an originalcaster angle calculating step of calculating an original caster angleθCAS by quantizing the caster angle formed by the measuring object linewith respect to a predetermined reference line based on the image data;and an effective data judging step for judging the original caster angleθCAS at the time of a change in value thereof to be the effective casterangle θECAS.

According to this embodiment, in the original caster angle calculatingstep, the original caster angle θCAS is calculated by quantizing thecaster angle formed by the measuring object line with respect to thepredetermined reference line based on the image data. In the effectivedata judging step, the original caster angle θCAS at the time of achange in value thereof is judged to be the effective caster angleθECAS. Although the caster angle is calculated in a non-contact mannerusing the image data outputted by the CCD camera, the measuring accuracyin measuring the caster angle can be maintained at a desired level.Thus, with the effective caster angle data θECAS, the wheel alignmentcan be quickly measured with a desired accuracy.

In a preferred embodiment of the present invention the caster anglemeasuring method for calculating an effective caster angle θECAS havinga desired measuring accuracy based on image data is obtained throughimage pick-up, by an external CCD camera, of a caster angle measuringobject line drawn on a wheel alignment measuring target plate attachedto a vehicle. This caster angle measuring method comprises: an originalcaster angle calculating step of calculating an original caster angleθCAS based on the image data when the caster angle formed by themeasuring object line with respect to a predetermined reference lineconstantly increases or decreases; a comparing step of comparing anoriginal caster angle θCAS(n−1) in the previous measurement with anoriginal caster angle θCAS(n) in the current measurement; and aneffective data judging step of judging the current original caster angleθCAS(n) to be the effective caster angle θECAS when the previousoriginal caster angle θCAS(n−1) is not equal to the current originalcaster angle θCAS(n) as a result of the comparison.

According to this embodiment, in the original caster angle calculatingstep, the original caster angle θCAS is calculated based on the imagedata when the caster angle formed by the measuring object line withrespect to the predetermined reference line constantly increases ordecreases. In the comparing step, the original caster angle θCAS(n−1) inthe previous measurement is compared with the original caster angleθCAS(n) in the current measurement. In the effective data judging step,the current original caster angle θCAS(n) is judged to be the effectivecaster angle θECAS when the previous original caster angle θCAS(n−1) isnot equal to the current original caster angle θCAS(n) as a result ofthe comparison. Although the caster angle is calculated in a non-contactmanner using the image data outputted by the CCD camera, the measuringaccuracy in measuring the caster angle can be maintained at a desiredlevel. Thus, with the effective caster angle data θECAS, the wheelalignment can be quickly measured with a desired accuracy.

In a preferred embodiment of the present invention the original casterangle calculating step comprises: a line extracting step of extractingthe measuring object line based on the image data; and an inclinationcalculating step of calculating-the inclination of the measuring objectline extracted by the method of least squares.

According to this embodiment, in the line extracting step, the measuringobject line is extracted based on the image data. In the inclinationcalculating step, the inclination of the extracted measuring object lineis calculated by the method of least squares. Thus, the effective casterangle data θECAS can be calculated speedily and accurately.

In a preferred embodiment of the present invention the original casterangle calculating step comprises: a line extracting step of extractingthe measuring object line based on the image data; and an inclinationcalculating step of calculating the inclination of the measuring objectline extracted by the method of least squares.

According to this embodiment, in the line extracting step, the measuringobject line is extracted based on the image data. In the inclinationcalculating step, the inclination of the extracted measuring object lineis calculated by the method of least squares. Thus, the effective casterangle data θECAS can be calculated speedily and accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprises: an image pick-up step of picking up an imageof a caster angle measuring object line drawn on a wheel alignmentmeasuring target plate attached to a vehicle; an original caster anglecalculating step of calculating an original caster angle θCAS byquantizing the caster angle formed by the picked-up measuring objectline with respect to a predetermined reference line; an effective datajudging step of judging the original caster angle θCAS at the time of achange in value thereof to be effective caster angle θECAS; and a datacomparing step of comparing the effective caster angle θECAS withmeasuring data of another dimension at substantially the same time thatthere is a change in the original caster angle θCAS.

According to this embodiment, in the image pick-up step, an image of thecaster angel measuring object line drawn on the wheel alignmentmeasuring target plate attached to the vehicle is picked up. In theoriginal caster angle calculating step, the original caster angle θCASis calculated by quantizing the caster angle formed by the picked-upmeasuring object line with respect to the predetermined reference line.In the effective data judging step, the original caster angle θCAS atthe time of a change in value thereof is judged to be the effectivecaster angle θECAS. In the data comparing step, the effective casterangle θECAS is compared with the measuring data of another dimension atsubstantially the same time that there is a change in the originalcaster angle θCAS. Thus, various data in wheel alignment measurement canbe compared with the caster angle data with a desired accuracy.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprises: an image pick-up step of picking up an imageof a caster angle measuring object line drawn on a wheel alignmentmeasuring target plate attached to a vehicle; an original caster anglecalculating step of calculating an original caster angle when the casterangle formed by the picked-up measuring object line with respect to apredetermined reference line constantly increases or decreases; acomparing step of comparing an original caster angle θCAS(n−1) in theprevious measurement with an original caster angle θCAS(n) in thecurrent measurement; an effective data judging step of judging thecurrent original caster angle θCAS(n) to be effective caster angle θECASwhen the previous original caster angle θCAS(n−1) is not equal to thecurrent original caster angle θCAS(n) as a result of the comparison; anda data comparing step of comparing the current original caster angleθCAS(n) with measuring data of another dimension measured atsubstantially the same time as the measurement of the current originalcaster angle θCAS(n).

According to this embodiment, in the image pick-up step, an image of thecaster angle measuring object line drawn on the wheel alignmentmeasuring target plate attached to the vehicle is picked up. In theoriginal caster angle calculating step, the original caster angle iscalculated when the caster angle formed by the picked-up measuringobject line with respect to the predetermined reference line constantlyincreases or decreases. In the comparing step, the original caster angleθCAS(n−1) in the previous measurement is compared with the originalcaster angle θCAS(n) in the current measurement. In the effective datajudging step, the current original caster angle θCAS(n) is judged to bethe effective caster angle θECAS when the previous original caster angleθCAS(n−1) is not equal to the current original caster angle θCAS(n) as aresult of the comparison. In the data comparing step, the currentoriginal caster angle θCAS(n) is compared with the measuring data ofanother dimension measured at substantially the same time as themeasurement of the current original caster angle θCAS(n). Thus, variousdata in wheel alignment measurement can be compared with the casterangle data with a desired accuracy.

To achieve the fifth object, the present invention provides a measuringplate characterized by a measuring surface on which are drawn: a firstreference mark whose center coordinates are situated at a predeterminedorigin; a plurality of second reference marks each having centercoordinates situated at the intersections of first virtual lines andsecond virtual lines; and a plurality of correction lines which are inparallel with either the first virtual lines or the second virtual linesand situated at fixed intervals. The first virtual lines are in parallelwith each other, and the second virtual lines are perpendicular to thefirst virtual lines and in parallel with each other. The predeterminedorigin corresponds to the center of the rotational axis of a wheel of avehicle being measured.

According to this embodiment, the first reference mark, the secondreference marks, and the correction lines are drawn on the measuringsurface of the measuring plate. The center coordinates of the firstreference mark are situated at the predetermined origin. The centercoordinates of each second reference mark are situated at theintersection of a first virtual line and a second virtual line. Themeasuring plate is attached to the wheel of the vehicle so that theorigin corresponds to the center of the rotational axis of the wheel.Any position on the picked-up image can be easily detected in therelative positional relationship with the center of the rotational axisof the wheel of the measured vehicle, and displacement (suspensionproperties or wheel alignment properties) of the rotational axis of thewheel can be measured at high speed in a large area of a threedimensional space in a constant and non-contact manner. Also, theposition coordinates can be calculated with accuracy based on the secondpick-up signal, regardless of the position of the measuring plate.

In a preferred embodiment of the measuring plate the first referencemark, the second reference marks, and the correction lines are indifferent colors from each other.

In this embodiment, the first reference mark, the second referencemarks, and the correction lines are in different colors from each other.Thus, they are easily distinguishable in image processing of thepicked-up image, and measurements can be taken speedily and accurately.

In a preferred embodiment of the measuring plate the first referencemark and the second reference marks are colored red, green, or blue.

According to this embodiment, the first reference mark and the secondreference marks are colored red, green, or blue. By performing colorseparation in image processing, the reference marks can be easily andquickly distinguished without requiring complicated data processing.

In a preferred embodiment of the measuring plate the remaining area onthe measuring surface, except for the first reference mark, the secondreference marks, and the correction lines, is a base area which iscolored black or white. The correction lines are colored black or white,whichever is different from the base area.

According to this embodiment, the base area is colored black or white,and the correction lines are black or white, whichever is different fromthe color of the base area. Thus, the correction lines can be easilydistinguished by binary processing, and the image processing can beperformed at high speed, which enables accurate wheel alignmentmeasurement.

In a preferred embodiment of the measuring plate the first referencemark is painted in a different color from the color of a vehicle beingmeasured.

According to this embodiment, the first reference mark is painted in adifferent color from the color of the vehicle, so that the color of thevehicle will not be mistaken for the first reference mark. Thus,accurate measurements can be taken.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device for measuring wheel alignment using the measuring platecomprises: a first image pick-up unit for outputting a first picked-upimage signal by picking up an image of a first area including the firstreference mark and the second reference marks on the measuring surfaceof the measuring plate; a second image pick-up unit for outputting asecond picked-up image signal by picking up an image of a second areasmaller than the first area and included in the first area, the secondimage pick-up unit having an optical axis situated in a positionpredetermined with respect to the optical axis of the first imagepick-up unit; a selecting unit for selecting one of the second referencemarks included in the second area based on the second picked-up imagesignal; a relative reference position calculating unit for calculatingthe position coordinates of the selected second reference mark asrelative reference position coordinates after specifying the selectedsecond reference mark within the first area based on the first picked-upimage signal; and a position calculating unit for calculating originreference position coordinates which are the position coordinates of theorigin in a predetermined position within the second area based on thesecond picked-up image signal and the relative reference positioncoordinates.

According to this embodiment, the first image pick-up unit outputs thefirst picked-up image signal to the relative reference positioncalculating unit by picking up an image of the first area including thefirst reference mark and the second reference marks on the measuringsurface of the measuring plate. The second image pick-up unit outputsthe second picked-up image signal to the selecting unit and the positioncalculating unit by picking up an image of the second area smaller thanthe first area and included in the first area. The selecting unitselects one of the second reference marks included in the second areabased on the second picked-up image signal. The relative referenceposition calculating unit specifies the selected second reference markwithin the first area based on the first picked-up image signal, andcalculates the position coordinates of the selected second referencemark as the relative reference position coordinates. The positioncalculating unit calculates the origin reference position coordinateswhich are the position coordinates of the origin in the predeterminedposition within the second area based on the second picked-up imagesignal and the relative reference position coordinates. Thus, the wheelalignment can be constantly and highly accurately measured in a largearea in a three dimensional space in a non-contact manner.

In a preferred embodiment of the present invention the selecting unitselects a second reference mark which is the closest to thepredetermined position in the second area.

According to this embodiment, the selecting unit selects a secondreference mark which is the closest to the predetermined position in thesecond area. Thus, the original position reference position coordinatescan be calculated with a smaller error, and the wheel alignment can bemeasured more accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises a color separation unit whichreceives the first picked-up image signal and the second picked-up imagesignal, performs color separation, and outputs a first color separationpicked-up image signal consisting of a first red picked-up image signal,a first green picked-up image signal, and a first blue picked-up imagesignal, and a second color separation picked-up image signal consistingof a second red picked-up image signal, a second green picked-up imagesignal, and a second blue picked-up image signal. The selecting unitspecifies the selected second reference mark based on the second colorseparation picked-up image signal, and the relative reference positioncalculating unit calculates the relative reference position coordinatesbased on the first color separation picked-up image signal.

According to this embodiment, the color separation unit receives thefirst picked-up image signal and the second picked-up image signal,performs color separation, and then outputs the first color separationpicked-up image signal consisting of the first red picked-up imagesignal, the first green picked-up image signal, and the first bluepicked-up image signal, and the second red picked-up image signal, thesecond green picked-up image signal, and the second blue picked-up imagesignal. The selecting unit specifies the selected second reference markbased on the second color separation picked-up image signal. Therelative reference position calculating unit calculates the relativereference position coordinates based on the first color separationpicked-up image signal. Thus, the image processing can be simplified,and the wheel alignment can be measured at high speed.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises a color separation unit whichreceives the first picked-up image signal and the second picked-up imagesignal, performs color separation, and outputs a first color separationpicked-up image signal consisting of a first red picked-up image signal,a first green picked-up image signal, and a first blue picked-up imagesignal, and a second color separation picked-up image signal consistingof a second red picked-up image signal, a second green picked-up imagesignal, and a second blue picked-up image signal. The selecting unitspecifies the selected second reference mark based on the second colorseparation picked-up image signal, and the relative reference positioncalculating unit calculates the relative reference position coordinatesbased on the first color separation picked-up image signal.

According to this embodiment, the color separation unit receives thefirst picked-up image signal and the second picked-up image signal, andperforms color separation. The color separation unit then outputs thefirst color separation picked-up image signal consisting of the firstred picked-up image signal, the first green picked-up image signal, andthe first blue picked-up image signal to the relative reference positioncalculating unit, and the second color separation picked-up image signalconsisting of the second red picked-up image signal, the second greenpicked-up image signal, and the second blue picked-up image signal tothe selecting unit.

The selecting unit specifies the selected second reference mark based onthe second color separation picked-up image signal, and the relativereference position calculating unit calculates the relative referenceposition coordinates based on the first color separation picked-up imagesignal.

In a preferred embodiment of the present invention the relativereference position calculating unit comprises a center positioncalculating unit which calculates the center position coordinates of theselected second reference mark as the relative reference positioncoordinates based on the second color separation picked-up image signal.The position calculating unit comprises: a relative position coordinatecalculating unit for calculating the relative position coordinates ofthe predetermined position relative to the relative reference positioncoordinates; and an origin reference position coordinate calculatingunit for calculating the origin position reference position coordinatesby adding the relative position coordinates to the center positioncoordinates of the selected second reference mark.

According to this embodiment, the center position calculating unit ofthe relative reference position calculating unit calculates the centerposition coordinates of the selected second reference mark as therelative reference position coordinates based on the second colorseparation picked-up image signal. The relative position coordinatecalculating unit calculates the relative position coordinates of thepredetermined position relative to the relative reference positioncoordinates. The origin reference position coordinate calculating unitcalculates the origin position reference position coordinates by addingthe relative position coordinates to the center position coordinates ofthe selected second reference mark. Thus, the center position of theselected second reference mark, i.e., the wheel alignment of thevehicle, can be quickly measured with a high accuracy based on thesecond picked-up image.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises: a plurality of distance sensorswhich measure the distances from different positions on the measuringsurface of the measuring plate, and outputs measuring signals; and adistance calculating unit for calculating the distance from themeasuring surface and the camber angle based on the measuring signalsfrom the plurality of distance sensors.

According to this embodiment, the distance calculating unit calculatesthe distance from the measuring surface based on the measuring signalsoutputted from the plurality of the distance sensors that measure thedistances from different positions on the measuring surface of themeasuring plate. Thus, the distance from the measuring surface and thecamber angle can be calculated speedily and accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprises: a first image picked-up step of picking upan image of a first area containing the first reference mark and thesecond reference marks on the measuring surface of the measuring plate;a second image pick-up step of picking up an image of a second areasmaller than the first area and included in the second area; a selectingstep of selecting one of the second reference marks included within thesecond area as a selected second reference mark; a relative referenceposition calculating step of calculating relative reference positioncoordinates which are the position coordinates of the selected secondreference mark specified in the first area; and a position calculatingstep of calculating origin position reference position coordinates whichare the position coordinates of the origin of a predetermined positionin the second area, based on the relative reference positioncoordinates.

According to this embodiment, in the first image pick-up step, an imageof the first area containing the first reference mark and the secondreference marks on the measuring surface of the measuring plate ispicked up. In the second image pick-up step, an image of the second areasmaller than the first area and included in the second area is pickedup. In the selecting step, one of the second reference marks includedwithin the second area is selected as the selected second referencemark. In the relative reference position calculating step, the relativereference position coordinates, which are the position coordinates ofthe selected second reference mark specified in the first area, arecalculated. In the position calculating step, the origin positionreference position coordinates, which are the position coordinates ofthe origin of the predetermined position in the second area, arecalculated based on the relative reference position coordinates. Thus,the position of any point on the picked-up image can be detected inrelation with the center of the rotational axis of the wheel of thevehicle being measured, and displacement (suspension properties or wheelalignment properties) of the rotational axis of the wheel is constantlymeasured at speed in a large area in a three-dimensional space in anon-contact manner. Also, the position coordinates can be calculatedwith accuracy based on the second picked-up image signal, regardless ofthe position of the measuring plate.

In a preferred embodiment of the present invention the selected secondreference mark is the second reference mark closest to the predeterminedposition among the second reference marks in the second area in theselecting step.

According to this embodiment, in the selecting step, the secondreference mark closest to the predetermined position is selected as theselected second reference mark among the second reference marks in thesecond area. Thus, the origin position reference position coordinatescan be calculated with a smaller error.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises a color separation step of performingcolor separation on the images picked up in the first image pick-up stepand the second image pick-up step so as to generate a first colorseparation picked-up image and a second color separation picked-upimage. In the selecting step, the selected second reference mark isspecified based on the second color separation picked-up image. In therelative reference position calculating step, the relative referenceposition coordinates are calculated based on the first color separationpicked-up image.

According to this embodiment, in the color separation step, colorseparation is performed on the images picked up in the first imagepick-up step and the second image pick-up step so as to generate thefirst color separation picked-up image and the second color separationpicked-up image. In the selecting step, the selected second referencemark is specified based on the second color separation picked-up image.In the relative reference position calculating step, the relativereference position coordinates are calculated based on the first colorseparation picked-up image. Thus, the image processing can besimplified, and the wheel alignment can be easily and quickly measured.

In a preferred embodiment of the present invention the relativereference position calculating step comprises a center positioncalculating step of calculating the relative reference positioncoordinates, which are the center position coordinates of the selectedsecond reference mark, based on the second color separation picked-upimage. Also, the position calculating step comprises: a relativeposition coordinate calculating step of calculating the relativeposition coordinates of the predetermined position with respect to therelative reference position coordinates; and an origin referenceposition coordinate calculating step of calculating the origin positionreference position coordinates by adding the relative positioncoordinates to the center position coordinates of the selected secondreference mark.

According to this embodiment, in the center position calculating step,the relative reference position coordinates, which are the centerposition coordinates of the selected second reference mark, arecalculated based on the second color separation picked-up image. In therelative position coordinate calculating step, the relative positioncoordinates of the predetermined position with respect to the relativereference position coordinates are calculated. In the origin referenceposition coordinate calculating step, the origin position referenceposition coordinates are calculated by adding the relative positioncoordinates to the center position coordinates of the selected secondreference mark. Thus, the center position of the selected secondreference mark can be detected with a high accuracy based on the secondpicked-up image signal, and the wheel alignment of the vehicle can bespeedily and highly accurately measured.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method further comprises: a distance measuring step ofmeasuring the distances from different positions on the measuringsurface of the measuring plate; and a distance calculating step ofcalculating the distance from the measuring surface and the camber anglebased on the distances measured in the distance measuring step.

According to this embodiment, in the distance measuring step, thedistances from different positions on the measuring surface of themeasuring plate are measured. In the distance calculating step, thedistance from the measuring surface and the camber angle are calculatedbased on the distances measured in the distance measuring step.

To achieve the sixth object, a preferred embodiment of the presentinvention provides a measuring plate characterized by having a measuringsurface on which a plurality of concentric circles having apredetermined origin and grid scale lines are drawn, and being attachedto a wheel of a vehicle being measured so that the origin corresponds tothe center of the rotational axis of the wheel.

According to this embodiment, a plurality of concentric circles havingthe predetermined origin and grid scale lines are drawn on the measuringsurface, and the position of the origin corresponds to the center of therotational axis of the vehicle. A concentric circle whose image ispicked up with the measuring plate is specified based on its curvature.The measuring object position relative to the rotational axis of thewheel can be speedily and accurately calculated based on the positionalrelationship between the concentric circle and the grid scale lines.Thus, the wheel alignment can be speedily and accurately measured, andthe reproducibility and reliability of the measurement can be improved.

In a preferred embodiment of the present invention the scale linescomprise first scale lines in parallel with each other, and second scalelines perpendicular to the first scale lines and in parallel with eachother, and the concentric circles and the first and second scale linesare drawn in different colors.

According to this embodiment, the concentric circles, the first scalelines, and the second scale lines are drawn in different colors, so thateach of them can be easily distinguished, and that the measuring objectposition can be accurately detected.

In a preferred embodiment of the present invention the concentriccircles and the first and second scale lines are colored red, green, orblue.

According to this embodiment, the concentric circles and the first andsecond scale lines are colored red, green, or blue, and color separationby three primary colors is performed to distinguish them. Thus, thepositions can be speedily and accurately measured, and the wheelalignment can also be speedily and accurately measured.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device comprises: an image pick-up unit for picking up animage of the measuring surface so that at least a part of at least oneof the concentric circles and at least a part of the scale lines areincluded in the picked-up image; a judging unit for judging whichconcentric circle is included in the image picked up by the imagepick-up unit based on the curvature of the concentric circle in thepicked-up image; a scale line specifying unit for specifying the scalelines included in the picked-up image based on the judgrnent made by thejudging unit; and an operation unit for calculating the position on themeasuring plate corresponding to a measuring object position, based onthe positional relationship between the specified scale lines and themeasuring object position in the image picked up by the image pick-upunit.

According to this embodiment, the image pick-up unit picks up an imageof the measuring surface at least a part of at least one of theconcentric circles and at least a part of the scale lines are includedin the picked-up image. The judging unit judges which concentric circleis included in the image picked up by the image pick-up unit based onthe curvature of the concentric circle in the picked-up image. The scaleline specifying unit specifies the scale lines included in the picked-upimage based on the judgment made by the judging unit. The operation unitcalculates the position of the measuring plate corresponding to themeasuring object position, based on the positional relationship betweenthe specified scale lines and the measuring object position in the imagepicked up by the image pick-up unit. Thus, the position on the measuringplate corresponding to the measuring object position can be accuratelycalculated, and wheel alignment measurements of high reproducibility andreliability can be accurately taken.

In a preferred embodiment of the present invention the judging unitcomprises: a storing unit for storing the curvatures of the concentriccircles in advance; a concentric circle extracting unit for extracting aconcentric circle contained in the picked-up image based on outputsignals from the image pick-up unit; a curvature calculating unit forcalculating the curvature of the extracted concentric circle; and aconcentric circle specifying unit for specifying the concentric circleby comparing the curvature obtained by the curvature calculating unitwith the curvatures stored in the storing unit.

According to this embodiment, the storing unit stores the curvatures ofthe concentric circles, and the concentric circle extracting unitextracts the concentric circle included in the picked-up image based onthe curvature of the concentric circle and the output signal of theimage pick-up unit. The curvature calculating unit calculates thecurvature of the extracted concentric circle, and the concentric circlespecifying unit specifies the concentric circle by comparing thecurvature obtained by the curvature calculating unit with the curvaturesstored in the storing unit. Thus, the concentric circle can be surelyand accurately specified, and the measuring object position can beaccurately measured.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device comprises: an image pick-up unit for outputtingpicked-up image data by picking up an image of the measuring surface sothat at least a part of at least one of the concentric circles and atleast a part of the scale lines are included in the picked-up image; acolor separation unit for outputting color separation picked-up imagedata by performing color separation on the picked-up image data; ajudging unit for judging which concentric circle is included in theimage picked up by the image pick-up unit based on the color separationpicked-up image data and the curvature of the concentric circle in thepicked-up image; a scale line specifying unit for specifying the scalelines included in the picked-up image based on the judgment made by thejudging unit and the color separation picked-up image data; and anoperation unit for calculating the position on the measuring platecorresponding to a measuring object position, based on the positionalrelationship between the specified scale lines and the measuring objectposition in the image picked up by the image pick-up unit.

According to this embodiment, the image pick-up unit picks up an imageof the measuring surface so that at least a part of at least one of theconcentric circles and at least a part of the scale lines are includedin the picked-up image, and then outputs picked-up image data to thecolor separation unit. The color separation unit performs colorseparation on the picked-up image data, and outputs color separationpicked-up image data to the judging unit. The judging unit judges whichconcentric circle is included in the image picked up by the imagepick-up unit based on the color separation picked-up image data and thecurvature of the concentric circle in the picked-up image. The scaleline specifying unit specifies the scale lines included in the picked-upimage based on the judgment made by the judging unit and the colorseparation picked-up image data. The operation unit calculates theposition on the measuring plate corresponding to the measuring objectposition based on the positional relationship between the specifiedscale lines and the measuring object position in the image picked up bythe image pick-up unit. Thus, the position on the measuring platecorresponding to the measuring object position can be speedily andaccurately calculated, and as a result, accurate wheel alignmentmeasurements of high reproducibility and reliability can be accuratelytaken.

In a preferred embodiment of the present invention the judging unitcomprises: a storing unit for storing the curvatures of the concentriccircles in advance; a concentric circle extracting unit for extracting aconcentric circle included in the picked-up image based on the colorseparation picked-up image data; a curvature calculating unit forcalculating the curvature of the extracted concentric circle; and aconcentric circle specifying unit for specifying the concentric circleby comparing the curvature obtained by the curvature calculating unitwith the curvatures stored in the storing unit.

According to this embodiment, the storing unit stores the curvatures ofthe concentric circles in advance, and the concentric extracting unitextracts the concentric circle included in the picked-up image based onthe color separation picked-up image data The curvature calculating unitcalculates the curvature of the extracted concentric circle, and theconcentric circle specifying unit specifies the concentric circle bycomparing the curvature obtained by the curvature calculating unit withthe curvatures stored in the storing unit. Thus, the concentric circlecan be specified speedily and accurately.

In a preferred embodiment of the present invention the wheel alignmentmeasuring device further comprises a spin angle calculating unit forcalculating a spin angle by determining the inclination of the scalelines included in the picked-up image with respect to a predeterminedreference position.

According to this embodiment, the spin angle calculating unit calculatesa spin angle by determining the inclination of the scale lines includedin the picked-up image with respect to the predetermined referenceposition. Thus, the spin angle can be speedily and accuratelycalculated.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprises: an image pick-up step of picking up an imageof the measuring surface so that at least a part of at least oneconcentric circles and at least a part of the scale lines are includedin the picked-up image; a judging unit of judging which concentriccircle is included in the picked-up image based on the curvature of theconcentric circle included in the picked-up image; a scale linespecifying step of specifying the scale lines included in the picked-upimage based on the judgment made in the judging step; and an operationstep of calculating the position on the measuring plate corresponding toa measuring object position, based on the positional relationshipbetween the specified scale lines and the measuring object position inthe picked-up image.

According to this embodiment, in the image pick-up step, an image of themeasuring surface is picked up so that at least a part of at least oneconcentric circles and at least a part of the scale lines are includedin the picked-up image. In the judging step, which concentric circle isincluded in the picked-up image is judged based on the curvature of theconcentric circle included in the picked-up image. In the scale linespecifying step, the scale lines included in the picked-up image arespecified based on the judgment made in the judging step. In theoperation step, the position on the measuring plate corresponding to themeasuring object position is calculated based on the positionalrelationship between the specified scale lines and the measuring objectposition in the picked-up image. Thus, the position on the measuringplate corresponding to the measuring object position can be speedily andaccurately detected. As a result, the measuring time required for wheelalignment measurement can be shortened, which improves the measuringefficiency and the reliability in measurement.

In a preferred embodiment of the present invention the judging unitcomprises: a concentric circle extracting step of extracting aconcentric circle included in the picked-up image based on the picked-upimage data; a curvature calculating step of calculating the curvature ofthe extracted concentric circle; and a concentric specifying step ofspecifying the concentric circle by comparing the curvature obtained inthe curvature calculating step with the curvatures stored in advance.

According to this embodiment, in the concentric circle extracting step,the concentric circle included in the picked-up image is extracted basedon the picked-up image data. In the curvature calculating step, thecurvature of the extracted concentric circle is calculated. In theconcentric circle specifying step, the concentric circle is specified bycomparing the curvature obtained in the curvature calculating step withthe curvatures stored in advance. Thus, the concentric circle includedin the picked-up image can be surely specified, and the position can beaccurately specified. As a result, the wheel alignment can be accuratelymeasured.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method comprises: an image pick-up step of generatingpicked-up image data by picking up an image of the measuring surface sothat at least a part of at least one of the concentric circles and atleast a part of the scale lines are included in the picked-up image; acolor separation step of generating color separation picked-up imagedata by performing color separation on the picked-up image data; ajudging step of judging which concentric circle is included in the imagepicked up in the image pick-up step based on the color separationpicked-up image data and the curvature of the concentric circle in thepicked-up image; a scale line specifying step of specifying the scalelines included in the picked-up image based on the judgment made in thejudging step and the color separation picked-up image data; and anoperation step of calculating the position on the measuring platecorresponding to a measuring object position, based on the relationshipbetween the specified scale lines and the measuring object position inthe image picked up in the image pick-up step.

According to this embodiment, in the image pick-up step, an image of themeasuring surface is picked up so that at least a part of at least oneof the concentric circles and at least a part of the scale lines areincluded in the picked-up image, and picked-up image data are thengenerated. In the color separation step, color separation is performedon the picked-up image data so as to generate color separation picked-upimage data. In the judging step, which concentric circle is included inthe image picked up by the image pick-up unit is judged based on thecolor separation picked-up image data and the curvature of theconcentric circle in the picked-up image. In the scale line specifyingstep, the scale lines included in the picked-up image are specifiedbased on the judgment made in the judging step and the color separationpicked-up image data. In the operation step, the position on themeasuring plate corresponding to the measuring object position iscalculated based on the relationship between the specified scale linesand the measuring object position in the image picked up in the imagepick-up step. Thus, the position on the measuring plate corresponding tothe measuring object position can be speedily and accurately calculatedthrough image processing. This improves the measuring efficiency andreliability in the wheel alignment measurement.

In a preferred embodiment of the present invention the wheel alignmentmeasuring method further comprises a spin angle calculating step ofcalculating a spin angle by determining the inclination of the scalelines in the picked-up image with respect to a predetermined referenceposition.

According to this embodiment, in the spin angle calculating step, a spinangle is calculated by determining the inclination of the scale lines inthe picked-up image with respect to the predetermined referenceposition. Thus, the spin angle can be speedily and accurately calculatedin a simple manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the structure of a wheelalignment measuring device;

FIGS. 2A and 2B illustrate the measuring plate;

FIG. 3 is a perspective front view of the measuring plate;

FIG. 4 illustrates the measuring mark area of the measuring plate;

FIG. 5 is a perspective view illustrating the arrangement of themeasuring unit;

FIG. 6 is a side view of the measuring unit;

FIG. 7 is a front view of the measuring unit;

FIG. 8 is a block diagram illustrating the structure of the dataprocessing control unit;

FIG. 9 is a block diagram of the structure of the image pick-up unit;

FIGS. 10A and 10B illustrate the visual field of the color CCD camera ofthe image pick-up unit of FIG. 9;

FIG. 11 is a block diagram illustrating the structure of another imagepick-up unit;

FIGS. 12A and 12B illustrate the visual field of the color CCD camera ofthe image pick-up unit of FIG. 10;

FIGS. 13A to 13C illustrate the arrangements of the laser displacementgauges;

FIG. 14 is a flowchart of the measuring operations;

FIG. 15 is a flowchart of the preprocessing;

FIG. 16 illustrates the operation of the preprocessing;

FIG. 17 illustrates the operation of the preprocessing;

FIG. 18 illustrates the operation of the preprocessing;

FIG. 19 illustrates the image pick-up area of the color CCD camera 5A;

FIG. 20 illustrates the scanning of the first circular mark;

FIGS. 21A and 21B illustrate the scanning of the first circular mark;

FIG. 22 illustrates the calculation of the rotational center coordinatesof the wheel;

FIG. 23 illustrates the image pick-up area of the color CCD camera 5B;

FIG. 24 illustrates the wheel alignment measurement;

FIG. 25 illustrates the wheel alignment measurement;

FIG. 26 illustrates the wheel alignment measurement;

FIGS. 27A and 27B illustrate the measuring plate;

FIG. 28 is a perspective front view of the measuring plate;

FIG. 29 is a block diagram illustrating the structure of the dataprocessing control unit;

FIG. 30 is a flowchart of the measuring operation;

FIG. 31 illustrates the distance measurement;

FIG. 32 illustrates the toe angle θTOE measurement;

FIG. 33 is a block diagram illustrating the structure of the wheelalignment measuring device of the third embodiment;

FIGS. 34A and 34B illustrate the measuring plate;

FIG. 35 is a partial perspective view of the measuring unit;

FIG. 36 is a side view of the measuring unit;

FIG. 37 is a front view of the measuring unit;

FIG. 38 is a block diagram illustrating the structure of the dataprocessing control unit;

FIGS. 39A to 39C illustrate the arrangements of the laser displacementgauges;

FIG. 40 illustrates the arrangements of the laser displacement gauges;

FIGS. 41A and 41B illustrate the arrangements of the laser displacementgauges;

FIG. 42 is a flowchart of the measuring operation of the thirdembodiment;

FIG. 43 illustrates the calculation of the camber angle;

FIG. 44 illustrates the calculation of the camber angle;

FIG. 45 is a block diagram illustrating the structure of the wheelalignment measuring device of the fourth embodiment;

FIG. 46 is an external perspective view of the measuring unit;

FIG. 47 is a side view of the measuring unit;

FIG. 48 is a front view of the measuring unit;

FIG. 49 is a block diagram illustrating the structure of the Z-axisdirection controller;

FIG. 50 is a block diagram illustrating the structure of the X-axisdirection controller;

FIG. 51 illustrates the relationship between the deviation and thefrequency of the driving pulse signal;

FIG. 52 is a block diagram illustrating the structure of the dataprocessing control unit;

FIGS. 53A to 53C illustrate the arrangements of the laser displacementgauges;

FIG. 54 is a flowchart of the measuring operation of the fourthembodiment;

FIG. 55 is a flowchart of the measuring operation of the fifthembodiment;

FIG. 56 is a block diagram illustrating the structure of the dataprocessing control unit of the sixth embodiment;

FIG. 57 illustrates the inclination detection of the caster angledetecting line;

FIG. 58 illustrates the smallest caster angle;

FIGS. 59A to 59C illustrate the relationship between the variation ofthe caster angle data and the data of another dimension;

FIG. 60 illustrates the relationship between the effective caster angledata and the data of another dimension;

FIG. 61 illustrates the caster angle measuring conditions;

FIG. 62 is a flowchart of the measuring operation;

FIG. 63 is a block diagram illustrating the structure of the wheelalignment measuring device;

FIG. 64 is a front view of the measuring plate;

FIG. 65 is an external perspective view of the measuring unit;

FIG. 66 is a block diagram illustrating the structure of the processormain body;

FIG. 67 is a flowchart of the measuring operation;

FIG. 68 illustrates the operation in the case where one concentriccircle and two scale lines are included in the picked-up image; and

FIG. 69 illustrates the operation in the case where one concentriccircle and one scale line are included in the picked-up image.

DETAILED DESCRIPTION OF THE INVENTION

The following is a description of the preferred embodiments of thepresent invention, with reference to the accompanying drawings.

A: First Embodiment

Referring to the drawings, a first preferred embodiment of the presentinvention is as follows.

Structure of the Alignment Measuring Device

FIG. 1 is a block diagram outlining the structure of the wheel alignmentmeasuring device.

The wheel alignment measuring device 1 comprises: a measuring plate 4 tobe attached to a wheel 3 of a measured vehicle 2; a measuring unit 7which picks up the image of the measuring surface 4S of the measuringplate 4 with an image pick-up unit 5 equipped with two CCD camerascapable of picking up color images, and measures the distance from themeasuring surface 4S of the measuring plate 4 with two laserdisplacement gauges 6-1 and 6-2; and a data processing control unit 8which performs alignment operations based on output signals from themeasuring unit 7, and controls the measuring unit 7.

Structure of the Measuring Plate

FIGS. 2A and 2B show the measuring plate. FIG. 2A is a front view of themeasuring plate, and FIG. 2B is a side view of the measuring plate.

The measuring surface 4S of the measuring plate 4 is flat, and as shownin FIGS. 2A and 2B, it consists of a measuring mark area MRK on whichvarious measuring marks are drawn, and a distance measuring area MLAwhich extends in the longitudinal direction of the measured vehicle 2with respect to the origin O of the measuring mark area MRK, and isoptically uniform (i.e., uniform in reflectance) to measure the distancefrom the measuring surface 4S. Measuring light emitted from the laserdisplacement gauges 6-1 and 6-2 irradiates the distance measuring areaMLA.

The measuring mark area MRK consists of: a base BB which is coloredblack; a first circular mark MC1 which is colored red and serves as areference mark with the origin O of the measuring surface 4S at itscenter; a plurality of second circular marks MC2 which are colored blue;and a plurality of correction lines CL which are colored white. Theplurality of second circular marks MC2 have their center coordinates atthe intersections of first parallel virtual lines (only two firstvirtual lines VL11 and VL12 are shown in FIG. 2A) and second parallelvirtual lines (only two second virtual lines VL21 and VL22 are shown inFIG. 2A). The plurality of correction lines CL are in parallel witheither the first virtual lines or the second virtual lines (they are inparallel with the second virtual lines VL21 and VL22 in FIG. 2A), andtheir interval distances Δd are uniform.

As the circular marks MC1 and MC2, and the correction lines CL serve asmeasuring scales, they should be drawn with a certain precision so thatdesired accuracy can be achieved in measurement.

On the back of the measuring plate, as shown in FIG. 2B and theperspective front view of FIG. 3, a bracket HLD for attaching themeasuring plate 4 to the wheel 3 of the measured vehicle 2 is disposed.

FIG. 4 illustrates the measuring mark area MRK of the measuring plate 4in detail.

In the measuring mark area MRK, a distance Lx is invariably maintainedbetween the center of the first circular mark MC1 and the center of thenearest second circular mark MC2 in the direction of the arrow X, andbetween the center of one second circular mark MC2 and the center of thenearest second circular mark MC2 in the direction of the arrow X.

Also, a distance Lz is invariably maintained between the center of thefirst circular mark MC1 and the center of the nearest second circularmark MC2 in the direction of the arrow Z, and between the center of onesecond circular mark MC2 and the center of the nearest second circularmark MC2 in the direction of the arrow Z.

Here, the distances Lx and Lz are not necessarily equal. However, forease of arithmetic operations, it is preferable to set them equal(Lx=Lz).

A distance Δd is maintained between one correction line CL and thenearest correction line CL. Here, for ease of image processing, thedistance Δd is preferably equal to the distance Lz (Δd=Lz), and thedistance between one correction line CL and the center of the nearestsecond circular mark MC2 is preferably set at Δd/2(=Lz/2), so as toprevent the correction lines CL from overlapping with the first circularmark MC1 and the second circular marks MC2.

The first circular mark MC1 is used in roughness measurement, while thesecond circular marks MC2 are used in precision measurement. In view ofthis, the relationship between the diameter RMC1 of the first circularmark MC1 and the diameter RMC2 of each second circular mark MC2 ispreferably defined as

RMC 1≈2×RMC 2

wherein the size of the second circular mark MC2 is preferably 1 cm.

If the ultimate target precision is hundreds of microns, the dimensionaltolerance is preferably smaller than tens of microns.

Although the first circular mark MC1 is red, and the second circularmakes MC2 are blue in the above explanation, any of the three primarycolors, red, green, and blue, can be used in the processes describedlater.

To prevent errors in data processing, the first circular mark MC1preferably has a color which is not included in the picked-up image ofthe measured vehicle 2. More specifically, if the measured vehicle 2 isred, the first circular mark MC1 should be green, for instance.

Likewise, although the base BB is black, and the correction lines CL arewhite, the colors may be other way around in the image processingdescribed later.

In this embodiment, the first virtual lines VL11 and VL12 areperpendicular to the second virtual lines VL21 and VL22. However, theymay cross each other at a predetermined angle, though this makes thearithmetic operations more complicated.

Structure of the Measuring Unit

FIG. 5 is a partial perspective view of the measuring unit, FIG. 6 is aside view of the measuring unit, and FIG. 7 is a front view of themeasuring unit.

The measuring unit 7 comprises: a holding plate 10 which is rectangularand holds the two laser displacement gauges 6-1 and 6-2; and the imagepick-up unit 5 which is provided on the rear side of the measuring plate10 and picks up images of the measuring plate 4 through an opening 5A(shown in FIG. 7).

With the measuring plate 4 within the measurable area, the holding plate10 holds the laser irradiation surface LP of the laser displacementgauges 6-1 and 6-2 in such a position that measuring light can irradiatethe distance measuring area MLA of the measuring plate 4, even if themeasuring plate 4 is in a measuring plate position 4UP which is theuppermost position for the measuring plate 4, in a measuring plateposition 4DN which is the lowermost position for the measuring plate 4,in a measuring plate position 4FR which is the furthest front positionfor the measuring plate 4, or in a measuring plate position (not shown)which is the furthest rear position for the measuring plate 4.

Structure of the Data Processing Control Unit

FIG. 8 is a block diagram illustrating the structure of the dataprocessing control unit 8.

The data processing control unit 8 comprises a display 25, a colorseparating circuit 27, and an arithmetic operation unit 28. The display25 displays an image based on first picked-up image data DGG1 outputtedfrom a color CCD camera 5A (mentioned later) or second picked-up imagedata DGG2 outputted from a color CCD camera 5B. The color separationcircuit 27 performs color separation based on the first picked-up imagedata DGG1 and the second picked-up image data DGG2 outputted from theimage pick-up unit 5, and outputs red picked-up image data DRcorresponding to red, green picked-up image data DG corresponding togreen, and blue picked-up image data DB corresponding to blue. Thearithmetic operation unit 28 outputs: X-coordinate data X on themeasuring surface 4S of the measuring plate 4 in a predeterminedposition in a high-resolution picked-up image (for instance, the centerof the picked-up image); Y-coordinate data Y of the measuring surface4S; Z-coordinate data Z on the measuring surface 4S of the measuringplate 4 in a predetermined position in a high-solution picked-up image;an inclination θx with respect to the X-axis on the measuring surface4S; an inclination θy with respect to the Y-axis on the measuringsurface 4S; and an inclination θz with respect to the Z-axis on themeasuring surface 4S (these inclination data are used as a basis in spinangle data DSP operations), based on output signals DLD1 and DLD2 fromthe two laser displacement gauges 6-1 and 6-2, the red picked-up imagedata DR, the green picked-up image data DG, and the blue picked-up imagedata DB.

Here, the red picked-up image data DR include first red picked-up imagedata DR1 corresponding to the first picked-up image data DGG1 and secondred picked-up image data DR2 corresponding to the second picked-up imagedata DGG2; the green picked-up image data DG include first greenpicked-up image data DG1 corresponding to the first picked-up image dataDGG1 and second green picked-up image data DG2 corresponding to thesecond picked-up image data DGG2; and the blue picked-up image data DBinclude first blue picked-up image data DB1 corresponding to the firstpicked-up image data DGG1 and second blue picked-up image data DB2corresponding to the second picked-up image data DGG2.

Structure of the Image Pick-up Unit

FIG. 9 shows the structure of the image pick-up unit.

The image pick-up unit 5 comprises: a low-resolution color CCD camera 5Awhich has an optical axis inclined at a predetermined angle θCCD of fromthe optical axis of a color CCD camera 5B (described later), has avisual field ARA (shown in FIG. 10) on the measuring surface 4S of themeasuring plate 4, and outputs the first picked-up image data DGG1; anda high-resolution color CCD camera 5B which has an optical axisperpendicular to the measuring surface 4S of the measuring plate 4 inthe initial state, has a visual field ARB (shown in FIG. 10) on themeasuring surface 4S of the measuring plate 4, and outputs the secondpicked-up image data DGG2.

Here, the predetermined angle θCCD is set so that the Z-axis directiondifference ΔE between the optical axis of the color CCD camera 5A andthe optical axis of the color CCD camera 5B on the measuring surface 4Scan be within a predetermined error allowable range between the Y-axisfurthest front position 4SFR and the Y-axis furthest rear position 4SRRof the measuring surface 4S with respect to an initial referenceposition 4SREF in the Y-axis direction of the measuring surface 4S.

As can be seen from the perspective view of FIG. 10A and the front viewof FIG. 10B, the visual field ARB of the color CCD camera 5B is includedin the visual field ARA of the color CCD camera 5A, and the visual fieldof the color CCD camera 5A includes almost the entire measuring surface4S of the measuring plate 4.

Accordingly, if the color CCD cameras 5A and 5B both have the samenumber of pixels, the color CCD camera 5A picks up an image of a largearea, which results in a low-resolution image and position detectionwith low accuracy. On the other hand, the color CCD camera 5B picks upan image of a very small area, which leads to a high-resolution imageand accurate position detection.

Since the real distance from the measuring plate varies for each CCDcamera, it is necessary to perform distance correction for more accuratemeasurement.

Although a multiple optical axis system in which the optical axes of thetwo color CCD cameras 5A and 5B are not identical is employed in thisembodiment, a single optical axis system in which the optical axes ofcolor CCD cameras 5A′ and 5B′ are identical, as shown in FIG. 11, mayalso be employed.

More specifically, a half mirror 5C is disposed in the optical paths ofthe color CCD cameras 5A′ and 5 b′ so that the optical axes of thembecome identical.

As can be seen from the perspective view of FIG. 12A and the front viewof FIG. 12B, the visual field ARB of the color CCD camera 5B′ isincluded in the visual field ARA of the color CCD camera 5A′, and thevisual field ARA of the color CCD camera 5A′ includes almost the entiremeasuring surface 4S of the measuring plate 4.

Accordingly, no distance correction is necessary even for accuratemeasurement.

Whether in the multiple optical axis system or in the single opticalaxis system, an absolute relationship should be maintained between thepositions of the two color CCD cameras 5A′ and 5B′, and the relationshipnever change during measurement.

Arrangements of the Laser Displacement Gauges

FIG. 13 shows the arrangements of the laser displacement gauges. FIG.13A is a perspective view illustrating the arrangements of the laserdisplacement gauges, FIG. 13B is a side view of the laser displacementgauges in the initial state, and FIG. 13C is a side view illustratingthe laser displacement gauges in a measuring state.

As shown in FIGS. 13A and 13B, the laser displacement gauges 6-1 and 6-2are disposed so that the virtual line connecting the measuring lightirradiation point P1 of the laser displacement gauge 6-1 and themeasuring light irradiation point P2 of the laser displacement gauge 6-2includes the origin O, which is the center point of the first circularmark MC1.

Measuring Operation

The following is a description of measuring operations, with referenceto FIGS. 14 to 26.

FIG. 14 is a flowchart of measuring operations.

First, the wheel 3 of the measured vehicle 2 is first driven upward ordownward by an actuator (not shown), independently of other wheels. Theactuator is then stopped at the empty vehicle weight to maintain astopped state (step S1).

Next, preprocessing is performed as follows. The holding plate 10 andthe image pick-up unit 5 are driven in the Z-axis direction so that theyface to the measuring surface 4S of the measuring plate 4. The imagepick-up regions of the color CCD cameras 5A and 5B, which constitute theimage pick-up unit 5, are arranged to include the first circular markMC1. Also, the measuring surface 4S of the measuring plate is disposedin such a position that it is perpendicular to the optical axis of thecolor CCD camera 5B (step S2).

FIG. 15 is a flowchart of the preprocessing.

In the preprocessing, the center coordinates of the first circular markMC1 in the stopped state are calculated (the calculation method usedhere will be later described), and the calculated center coordinates areset as the initial mark coordinates (X00, Z00), which are the centercoordinates when the caster angle θCAS is 0°, as shown in FIG. 16 (stepS31).

The caster angle θCAS of the wheel is changed by rotating the wheel byhand in a first direction. The center coordinates of the first circularmark MC1 are again calculated with the caster angle θCAS being θ1, andthe calculated coordinates are set as first caster angle markcoordinates (X01, Z01) (step S32).

The wheel is then rotated by hand in a second direction, opposite to thefirst direction, and moved past the center coordinates of the firstcircular mark calculated as the initial mark coordinates (X00, Z00). Thecenter coordinates of the first circular mark MC1 are again calculatedwith the caster angle θCAS being θ2, and the calculated coordinates areset as a second caster angle mark coordinates (X02, Z02) (step S33).

The arithmetic operation unit 28 determines the equation of the circlethat includes the three points: the initial mark coordinates (X00, Z00);the first caster angle mark coordinates (X01, Z01); and the secondcaster angle mark coordinates (X02, Z02). Using the equation, thearithmetic operation unit 28 calculates the coordinates of the rotationaxis of the wheel (XX, ZZ) (step S34).

More specifically, the equation that includes the three points is givenas:

(X−XX)²+(Z−ZZ)² =r ²  (1)

The radius r of the circle (r is a constant corresponding to deviationof the center point), and the X-coordinate XX and the Z-coordinate ZZ ofthe rotation axis of the wheel can be obtained by substituting theinitial mark coordinate (X00, Z00), the first caster angle markcoordinate (X01, Z01), and the second caster angle mark coordinate (X02,Z02) for the variables X and Z.

The middle point MP of the viral line connecting the measuring laserirradiation points P1 and P2 of the laser displacement gauges 6-1 and6-2 coincides with the optical axis of the color CCD camera 5B. Thearithmetic operation circuit 2 calculates the mean distance from thecolor CCD camera 5A to the measuring plate 4 based on the output signalsDLD1 and DLD2 of the laser displacement gauges 6-1 and 6-2, and it alsocalculates the toe angel θTOE of the measuring plate 4 based on thedistances to the irradiation points P1 and P2.

More specifically, as shown in FIG. 17, the distance from the middlepoint MP. that is, the mean distance L4 to the measuring plate 4 isexpressed as:

L 4=(LY 1+LY 2)/2

wherein the distance from the distance measuring area MLA of themeasuring plate 4 corresponding to the output signal DLD1 of the laserdisplacement gauge 6-1 is LY1, and the distance from the distancemeasuring area MLA of the measuring plate 4 corresponding to the outputsignal DLD2 is LY2.

As shown in FIG. 18, the toe angle θTOE of the measuring plate 4 isexpressed as:

θTOE=tan⁻¹(|LY 1−LY 2|/LX)

In this situation, the relationship between the visual field ARA of thecolor CCD camera 5A and the visual field ARB of the color CCD camera 5Bis as in FIG. 10A or FIG. 12. The image pick-up unit 5 picks up an imageof the measuring surface 4S of the measuring plate 4 (step S3) andoutputs the first picked-up image data DGG1 and the second picked-upimage data DGG2 to the color separation circuit 27 of the processor mainbody 8A (step S4).

The color separation circuit 27 performs color separation respectivelyon the first picked-up image data DGG1 and the second picked-up imagedata DGG2 outputted from the image pick-up unit 5 under the control of acontroller 25, and then outputs the red picked-up image data DRcorresponding to red, the green picked-up image data DG corresponding togreen, and the blue picked-up image data DB corresponding to blue, tothe arithmetic operation unit 28 (step S5).

The following is a detailed description of the arithmetic operation,with reference to FIGS. 19 to 26.

In FIG. 19, the focal length of the lens of the color CCD camera 5A isf=f5A [mm], the number of pixels of the color CCD camera 5A is Nx×Nz[dots] (Nx and Nz are natural numbers. For instance, Nx=400, Nz=400).The color CCD camera 5A is disposed at a distance of Lf5A, whichcorresponds to the focal length f5A, from the measuring surface 4S, sothat the visual field ARA covers the region of L5A×L5A [mm]. Accordingto an equation Nx=Nz=NN (NN is a natural number), one pixel correspondsto L5A/NN [mm].

To determine the center coordinates of the Z-axis, as shown in FIG. 20,the first circular mark MC1 is detected by scanning in the positivedirection of the X-axis based on the first red picked-up image data DR1to conduct a rough search, starting from the center coordinates CCA ofthe color CCD camera 5A, in a first predetermined direction (forinstance, the positive direction of the Z-axis; upward in FIG. 20) atDN-dot intervals (equivalent to intervals of DN·L5A/NN [mm] in thiscase) (step S6). Here, the relationship between DN and the diameter RMC1of the first circular mark MC1 should be expressed as:

DN·L5A/NN≦RMC 1

After the detection of the first circular mark MC1 by the rough searchin step S6, a fine search is next conducted by scanning in a firstpredetermined direction (for instance, the positive direction of theX-axis; upward in FIG. 21A) at 1-dot intervals (equivalent to intervalsof L5A/NN[mm] in this case), as shown in FIG. 21A. This fine search iscontinued until the first circular mark MC1 becomes undetectable, andthe pixel number (dot number N1; N1=1 to NN) in the Z-axis direction isstored when the first circular mark MC1 is detected for the last time.

As shown in FIG. 21B, a fine search is then conducted in the oppositedirection from the first predetermined direction (for instance, in theZ-axis direction; downward in FIG. 21B) (step S7).

In step S7, when the first circular mark MC1 is no longer detected, theZ-axis center coordinate Z0′ is determined based on the pixel number(dot number N2; N2=1 to NN) in the Z-axis direction at the time of lastdetection of the first circular mark MC1 (step S8). The Z-axis centercoordinate Z0′ is given by an expression:

Z 0′=(N 1+N 2)/2

Here, the Z-axis center coordinate Z0′ is almost equal to theZ-coordinate of the center coordinates of the first circular mark MC1,and the accuracy of the Z-axis center coordinate Z0′ is ±L5A/NN [mm].

Likewise, in order to determine the X-axis center coordinate X0′, thefirst circular mark MC1 is detected by scanning in the positivedirection of the Z-axis based on the first red picked-up image data DR1so as to conduct a rough search in a third predetermined direction (forinstance, in the positive direction of the X-axis; rightward in FIG.20), starting from the center coordinates CCA of the color CCD camera5A, at DN-dot intervals (equivalent to intervals of DN·L5A/NN [mm])(step S9).

After the detection of the first circular mark MC1 by the rough searchin step S9, a fine search is conducted at 1-dot intervals (equivalent tointervals of L5A/NN [mm]), and it is continued until the first circularmark MC1 is no longer detected. The pixel number (dot number M1; M1=1 toNN) in the X-axis direction is stored when the first circular mark MC1is detected for the last time, and a fine search in the negativedirection of the X-axis is then conducted (step S10).

In step S10, when the first circular mark MC1 is no longer detectedagain, the X-axis center coordinate X0′ is determined based on the pixelnumber (dot number M2; M2=1 to NN) in the X-axis direction at the lastdetection of the first circular mark MC1 (step S11). The X-axis centercoordinate X0′ is given by an expression:

X 0′=(M 1+M 2)/2

Here, the accuracy of the X-axis center coordinate X0′ is ±L5A/NN [mm].

Calculation of the Rotational Center Coordinates of the Wheel

The arithmetic operation unit 28 calculates the caster angle θCAS basedon second inclination data DSL 2 outputted from a caster angle measuringinclination gauge SCAS (step S12), and then calculates the rotationalcenter coordinates (X0, Z0) of the wheel from the Z-axis centercoordinate Z0′ determined in step S8 and the X-axis center coordinateX0′ determined in step S11 (step S13).

In this example, the rotational center coordinates of the wheel movesfrom the initial rotational center coordinates (XX, ZZ) to (X0, Z0), andthe center coordinates of the first circular mark MC1 are (X0′, Z0′).

As the caster angle θCAS has already been calculated in step S12, thecenter coordinates (Z0″, Z0″) of the first circular mark MC1 when thewheel is not rotating are calculated by the following formulas:

X 0″=X 0′ cos θCAS+Z 0′ sin θCAS

Z 0″=−X 0′ sin θCAS+Z 0′ cos θCAS

When ΔX=X00−XX and ΔZ=Z00−ZZ, the rotational center coordinates (X0, Z0)of the wheel can be calculated by the following formulas:

X 0=X 0″−ΔX=X 0″−X 00+XX

Z 0=Z 0″−ΔZ=Z 0″−Z 00+ZZ

Since the rotational center coordinates can be calculated by simpleformulas as above, real time processing can be performed withoutcomplicating the control operations of the arithmetic operation unit 28in the data processing control unit 28.

Referring now to FIG. 23, the focal length of the lens of the color CCDcamera 5B is shown as f=f5B [mm], and the number of pixels of the colorCCD camera 5B is Nx×Nz [dots], which is the same as that of the colorCCD camera 5A. The color CCD camera 5B is disposed at a distance ofLf5B, corresponding to the focal length f5B, from the measuring surface4S, so that the visual field ARB can cover the area of L5B×L5B [mm].According to an equation Nx=Nz=NN (NN is a natural number), one pixelcorresponds to L5B/NN [mm] pitch.

Next, as shown in FIG. 24, the correction lines CL are subjected tosampling based on a white image obtained by adding the second redpicked-up image data DR2, the second green picked-up image data DG2, andthe second blue picked-up image data DB2 outputted from the color CCDcamera 5B. The inclination θ of the correction lines L is determined bythe method of least squares using the position data (step S14).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the current rotational center coordinates (X0, Z0) of the wheeldetermined in steps S8 and S11, and the center coordinates CCB of thevisual field ARB of the color CCD camera 5B is determined (step S15).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the approximate positionof the visual field ARB can be detected.

Besides the current rotational center coordinates (X0, Z0) of the wheeland the distance LL, the arithmetic operation unit 28 calculates thedistance L4 from the middle point between the irradiation point P1 andthe irradiation point P2 on the measuring surface 4S of the measuringplate 4, that is, the optical axis of the color CCD camera 5B (see FIG.17), based on the output signals DLD1 and DLD2 of the laser displacementgauges 6-1 and 6-2.

As a result, the magnification of the picked-up image can be detecteddepending on the distance between the color CCD camera B and themeasuring plate 4, and the real size of the image can be easily detectedand corrected in image processing.

Referring to FIGS. 25 and 26, the calculation of the center coordinatesof the visual field ARB will be described below.

First, in an image picked up by the color CCD camera 5A, the distance dabetween the center coordinates CCA of the visual field ARA and thecenter coordinates (X0, Z0) of the first circular mark MC1 is calculatedby the following formula (step S16):

da=(xa ² +ya ²)

Assuming a line in parallel with the correction lines CL extendingthrough the center coordinates of the visual field ARA, the angle θaformed by the line, the center coordinates of the visual field ARA, andthe center coordinates of the first circular mark MC1 are calculated bythe following formula (step S17):

θa=tan⁻¹(ya/xa)−θ0

Based on the distance da and the angle θa, a distance Xa and a distanceYa are calculated by the following formulas (step S18):

Xa=da×cos(θa)

Ya=da×sin(θa)

Next, based on the distances Xa and Ya, the position of the secondcircular mark MC2 n closest to the center coordinates of the visualfield ARA is calculated as follows (step S19):

nx=int(Xa/Lx)

ny=int(Ya/Lz)

wherein nx (a natural number) is the number of second circular markscounted from the first circular mark MC1 in the X direction, and ny (anatural number) is the number of second circular marks counted from thefirst circular mark MC1 in the Z direction. In FIG. 25, the closestsecond mark MC2 n is shown as nx=4 and ny=3. Also, int(R) is an integerwhich does not exceed R. Lx is the interval distance between secondcircular marks MC2 in the X-axis direction (see FIG. 4), while Lz is theinterval distance between second circular marks MC2 in the Z-axisdirection (see FIG. 4).

The distances Xb and Yb from the center coordinates of the secondcircular mark MC2 n closest to the center coordinates of the visualfield ARA to the center coordinates (X0, Z0) of the first circular markMC1 are calculated by the following formulas (step S20):

Xb=nx×Lx

Yb=ny×Lz

The distances Xb and Yb represent the values of accuracy correspondingto the drawing accuracy of the first circular mark MC1 and the secondcircular marks MC2.

Referring to FIG. 26, the distance dd (low accuracy) from the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARA to the center coordinates of thevisual field ARA, and the angle θi (low accuracy) with respect to theX-axis of the visual field ARA are calculated by the following formulas(step S21):

dd={(Xa−Xb)²+(Ya−Yb)²}

θi=tan⁻¹{(Ya−Yb)/(Xa−Xb)}+θ0

Here, “low accuracy” means the measurable accuracy based on picked-upimage data of the color CCD camera 5A (In the above example, theaccuracy is ±1 mm).

Based on the distance dd and the angle θi, the low accuracy distances Xiand Yi between the center coordinates of the visual field ARA and thesecond circular mark MC2 n closest to the center coordinates of thevisual field ARA are calculated by the following formulas (step S22):

Xi=dd×cos(θi)

Yi=dd×sin(θi)

Based on the low accuracy distances Xi and Yi, the center coordinates ofthe second circular mark MC2 n closest to the center coordinate of thevisual field ARB of the color CCD camera 5B are converted into a dotaddress (IX, IY) (step S23).

Here, the visual field ARB consists of NN×NN dots as described above.The dot address of the center coordinates of the visual field ARB in theX direction is NN/2, while the dot address in the Y direction is NN/2.Hence, the dot address (IX, IY) is given by the following equations:

IX=NN/2+Xi×Sn/Lx

IY=NN/2+Yi×Sn/Lz

wherein Sn represents the number of dots a millimeter.

Based on the distances Xb and Yb, the distance Db (high accuracy)between the center coordinates of the visual field ARB and the centercoordinates of the closest second circular mark MC2 n, and the angle θb(high accuracy) with respect to the X-axis of the visual field ARA arecalculated by the following formulas (step S24):

Db=(Xb ² +Yb ²)

θb=tan⁻¹(nYb/Xb)+θ0

Here, “high accuracy” means the measurable accuracy based on picked-upimage data of the color CCD camera 5B (In the above example, theaccuracy is ±L5B/NN mm).

Based on the distance Db and the angle θb, the high accuracy distancesXc and Yc between the center coordinates of the visual field ARB and thecenter coordinates of the closest second circular mark MC2 n arecalculated by the following formulas (step S25):

Xc=Db×cos(θb)

Yc=Db×sin(θb)

Based on the high accuracy distances Xc and Yc and the dot address (IX,IY), the center coordinates of the second circular mark MC2 n closest tothe center coordinate of the visual field ARB of the color CCD camera 5Bare converted into a dot address (X, Y) (step S26).

In this case, the visual field ARB consists of NN×NN dots as describedabove. The dot address of the center coordinates of the visual field ARBin the X direction is NN/2, while the dot address in the Y direction isNN/2. Hence, the dot address (X, Y) is given by the following equations:

X=Xc+(NN/2+IX)×Lx/Sn

Y=Yc+(NN/2−IY)×Lz/Sn

The dot address (X, Y) is then transformed to the system of coordinatesincluding the X-axis and Z-axis of the measuring surface 4S of themeasuring plate 4, and a dot address (x, y) in the system of coordinatesincluding the X-axis and Z-axis of the measuring surface 4S iscalculated (step S27). Here, the relationship between the dot address(X, Y) and the dot address (x, y) can be given by equations:

X=x/cos(θx)

Y=y/cos(θy)

From these equations, the dot address (x, y) can be given by equations:

x=X×cos(θx)

Y=y×cos(θy)

The arithmetic operation unit 28 then calculates the camber angle θCAMbased on first inclination data DSL 1 outputted from a camber anglemeasuring inclination gauge SCAM (step S28).

As described so far, according to the present invention, accurate wheelalignment measurements can be taken by real-time detection of therotational center of the wheel, without attaching the measuring plate inconformity to the rotational center in advance.

It is also unnecessary to attach a jig to the measuring plate to conformto the rotational center, which reduces the thickness of the measuringplate in the transverse direction of the measured vehicle. Thus, therotational radius of the wheel at the time of a toe angle change can besmaller, and the entire area of the measuring surface of the measuringplate can be effectively utilized.

Although no special skill is necessary in attachment of the measuringplate, accurate wheel alignment measurements can be taken withoutreducing the measurable area.

B: Second Embodiment

The following is a description of a second embodiment of the presentinvention, with reference to the accompanying drawings.

Since the main structure of the wheel alignment measuring device of thesecond embodiment is the same as in the first embodiment shown in FIG.1, no description of it will be given below.

Structure of the Measuring Plate

FIGS. 27A and 27B show the measuring plate. FIG. 27A is a front view ofthe measuring plate, and FIG. 27B is a side view of the measuring plate.

The measuring surface 4S of the measuring plate 4 is flat, and as shownin FIGS. 27A and 27B, it consists of a measuring mark area MRK on whichvarious measuring marks are drawn, and a distance measuring area MLAwhich extends in the longitudinal direction of the measured vehicle 2with respect to the origin O of the measuring mark area MRK, and isoptically uniform (i.e., uniform in reflectance) to measure the distancefrom the measuring surface 4S. Measuring light emitted from the laserdisplacement gauges 6-1 and 6-2 irradiates the distance measuring areaMLA.

The measuring mark area MRK consists of: a base BB which is coloredblack; a first circular mark MC1 which is colored red and serves as areference mark with the origin O of the measuring surface 4S in thecenter; a plurality of second circular marks MC2 which are colored blue;and a plurality of correction lines CL which are colored white.The,plurality of second circular marks MC2 have center coordinates atthe intersections of first parallel virtual lines (only two firstvirtual lines VL11 and VL12 are shown in FIG. 27A) and second parallelvirtual lines (only two second virtual lines VL21 and VL22 are shown inFIG. 27A). The plurality of correction lines CL are in parallel witheither of the first virtual lines VL11 and VL12 or the second virtuallines VL21 and VL22 (they are in parallel with the second virtual linesVL21 and VL22 in FIG. 27A), and their interval distances Δd are uniform.

As the circular marks MC1 and MC2, and the correction lines CL serve asmeasuring scales, they should be drawn with certain precision so thatdesired accuracy can be achieved in measurement.

As shown in FIG. 27B and the perspective front view of FIG. 28, abracket HLD for attaching the measuring plate 4 to the wheel 3 of themeasured vehicle 2, a camber angle measuring inclination gauge SCAMwhich outputs first inclination data DSL 1 used in measurement of thecamber angle of the wheel 3, and a caster angle measuring inclinationgauge SCAS which outputs second inclination data DSL 2 used inmeasurement of the caster angle of the wheel 3 are disposed on the backof the measuring plate.

The structure of the measuring mark area MRK of the measuring plate 4 isthe same as in the first embodiment shown in FIG. 4, and the structureof the measuring unit is the same as in the first embodiment shown inFIGS. 5 to 7.

Structure of the Data Processing Control Unit

FIG. 29 is a block diagram illustrating the structure of the dataprocessing control unit 8. Like reference numerals are allotted to likecomponents in FIG. 29 and FIG. 8 of the first embodiment.

The data processing control unit 8 comprises a display 25, a colorseparating circuit 27, and an arithmetic operation unit 28. The display25 displays an image based on first picked-up image data DGG1 outputtedfrom a color CCD camera 5A (mentioned later) or second picked-up imagedata DGG2 outputted from a color CCD camera 5B. The color separationcircuit 27 performs color separation based on the first picked-up imagedata DGG1 and the second picked-up image data DGG2 outputted from theimage pick-up unit 5, and outputs red picked-up image data DRcorresponding to red, green picked-up image data DG corresponding togreen, and blue picked-up image data DB corresponding to blue. Thearithmetic operation unit 28 outputs: X-coordinate data X on themeasuring surface 4S of the measuring plate 4 in a predeterminedposition in a high-resolution picked-up image (for instance, the centerof the picked-up image); Y-coordinate data Y of the measuring surface4S; Z-coordinate data Z on the measuring surface 4S of the measuringplate 4 in a predetermined position in the a high-solution picked-upimage; an inclination θx with respect to the X-axis on the measuringsurface 4S; an inclination θy with respect to the Z-axis on themeasuring surface 4S; and an inclination θz with respect to the Z-axison the measuring surface 4S (these inclination data are used as a basisin spin angle data DSP operations), based on output signals DLD1 andDLD2 from the two laser displacement gauges 6-1 and 6-2, the firstinclination data DSL1 outputted from the camber angle measuring gaugeSCAM, the second inclination data DSL2 outputted from the caster angleinclination gauge SCAS, the red picked-up image data DR, the greenpicked-up image data DG, and the blue picked-up image data DB.

Here, the red picked-up image data DR include first red picked-up imagedata DR1 corresponding to the first picked-up image data DGG1 and secondred picked-up image data DR2 corresponding to the second picked-up imagedata DGG2; the green picked-up image data DG include first greenpicked-up image data DG1 corresponding to the first picked-up image dataDGG1 and second green picked-up image data DG2 corresponding to thesecond picked-up image data DGG2; and the blue picked-up image data DBinclude first blue picked-up image data DB1 corresponding to the firstpicked-up image data DGG1 and second blue picked-up image data DB2corresponding to the second picked-up image data DGG2.

The structure of the image pick-up unit is the same as in the firstembodiment shown in FIGS. 9 to 12, and the arrangements of the laserdisplacement gauges are also the same as in the first embodiment shownin FIG. 13.

Measuring Operations

The following is a description of measuring operations, with referenceto FIGS. 30 and 31.

Here, the first circular mark MC1 should be always included in an imagepicked up by the color CCD camera 5A that constitutes the image pick-upunit 5, and the measuring plate 4 is attached to the wheel 3 of themeasured vehicle 2 so that the origin O of the measuring surface 4Scorresponds to the rotational center axis of the wheel 3.

FIG. 30 is a flowchart of the measuring operations. Like referencenumerals are allotted to like components in FIG. 30 and FIG. 14 of thefirst embodiment.

As in the first embodiment, the wheel 3 of the measured vehicle 2 isfirst driven upward or downward by an actuator (not shown),independently of other wheels. The actuator is then stopped at the emptyvehicle weight to maintain a stopped state (step S1).

The holding plate 10 and the image pick-up unit 5 are driven in theZ-axis direction, so that they face to the measuring surface 4S of themeasuring plate 4. Then, the optical axes of the color CCD cameras 5Aand 5B that constitute the image pick-up unit 5 are arranged in linewith the origin O of the measuring surface 4S (step S2A).

Because of this, the virtual line connecting the laser irradiationpoints P1 and P2 of the laser displacement gauges 6-1 and 6-2 includesthe origin O.

As a result, the arithmetic operation unit 28 can calculate the distancefrom the first circular mark MC1 on the measuring surface 4S of themeasuring plate 4, based on the output signals DLD1 and DLD2 of thelaser displacement gauges 6-1 and 6-2.

More specifically, assuming that the distance from the distancemeasuring area MLA of the measuring plate 4 corresponding to the outputsignal DLD1 of the laser displacement gauge 6-1 is LY1, and that thedistance from the distance measuring area MLA of the measuring plate 4corresponding to the output signal DLD2 is LY2, the distance LMC1 fromthe first circular mark MC1 can be expressed as:

LMC 1=(LY 1+LY 2)/2

As in the first embodiment, the following operations are carried out:picking up an image of the measuring surface 4S of the measuring plate 4by the image pick-up unit 5 (step S3); outputting the first picked-upimage data DGG1 and the second picked-up image data DGG2 to the colorseparation circuit 27 of the data processing control unit 8A (step S4);performing color separation on the first picked-up image data DGG1 andthe second picked-up image data DGG2 by the color separation circuit 27(step S5); detecting the first circular mark MC1 by conducting a roughsearch at DN-dot intervals (step S6); detecting the first circular markMC1 by conducting a fine search with a scan in the positive direction ofthe X-axis at 1-dot intervals (step S7); calculating the Z-axis centercoordinate Z0 (step S8); detecting the first circular mark MC1 byconducting a rough search at CN-dot intervals with a scan in thepositive direction of the Z-axis (step S9); and detecting the firstcircular mark MC1 by conducting a fine search in the positive directionof the X-axis at 1-dot intervals (equivalent to intervals of L5A/NN mm)until the first circular mark MC1 can no longer be detected, storing thedot number M1(=1 to NN) in the X-axis direction when the first circularmark MC1 is detected for the last time, and conducting a fine search ofthe first circular mark MC1 in the negative direction of the X-axis(step S10).

In step S10, when the first circular mark MC1 becomes undetectableagain, the X-axis center coordinate X0 is calculated by the followingformula (step S11A):

X 0=(M 1+M 2)/2

based on the dot number M2 (=1 to NN) in the X-axis direction when thefirst circular mark MC1 is detected for the last time. As a result, theaccuracy of the X-axis center coordinate X0 is ±L5A/NN mm.

Meanwhile, as shown in FIG. 18 of the first embodiment, the focal lengthof the lens of the color CCD camera 5B is set as f=f5B mm, and thenumber of pixels of the color CCD camera 5B is set as the same as thatof the color CCD camera 5A, which is Nx×Nz dots. The color CCD camera 5Bis disposed at a distance of Lf5b corresponding to the focal length f5Bfrom the measuring surface 4S, so that the visual field ARB can coverthe area of L5B×L5B mm. If Nx=Nz=NN (NN is a natural number), one pixelcorresponds to a pitch of L5B/NN mm.

As shown in FIG. 19 of the first embodiment, the correction lines CL aresubjected to sampling based on the white image obtained by adding thesecond red picked-up image data DR2, the second green picked-up imagedata DG2, and the second blue picked-up image data DB2 outputted fromthe color CCD camera 5B, and the inclination θ of the correction linesCL is calculated from the positional data by the method of least squares(step S12A).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the center coordinates of the first circular mark MC1 determinedin steps S8 and S11 and the center coordinates CCB of the visual fieldARB of the color CCD camera 5B is calculated (step S13A).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the position of the visualfield ARB can be roughly detected.

Besides the calculation of the center coordinates (X0, Z0) of the firstcircular mark MC1 and the distance LL, the arithmetic operation unit 28calculates the distance from the middle point between the irradiationpoints P1 and P2 on the measuring surface 4S of the measuring plate 4(i.e., the distance from the optical axis position of the color CCDcamera 5B) based on the output signals DLD1 and DLD2 of the laserdisplacement gauges 6-1 and 6-2 (step S14A).

The following is a detailed description of the calculation of thedistance from the optical axis position.

As shown in FIG. 31, the laser emitting portions P6-1 and P6-2 (thereference numerals P6-1 and P6-2 also indicate the positions of theemitting portions) of the laser displacement gauges 6-1 and 6-2 aredisposed on a virtual plane VPL which contains a virtual line VL inparallel with the vertical direction of the measured vehicle. Theemitting portions P6-1 and P6-2 are situated on a line perpendicular tothe virtual line VL and at the same distance from the virtual line VL.

In FIG. 31, the distance from the irradiation point Pa on the distancemeasuring area MLA of the measuring plate 4 corresponding to the outputsignal DLD1 of the laser displacement gauge 6-1 is LP1, and the distancefrom the irradiation point P2 on the distance measuring area MLA of themeasuring plate 4 corresponding to the output signal DLD2 of the laserdisplacement gauge 6-2. Here, the distance LPP from the middle pointbetween the irradiation points P1 and P2, i.e., from the optical axisposition of the color CCD camera 5B is expressed as:

LPP=(LP 1+LP 2)/2

As a result, the magnification of the picked-up image can be detecteddepending on the distance between the color CCD camera B and themeasuring plate 4, and the real size of the image can be easily detectedand corrected in image processing.

Toe Angle Measurement

While calculating the distance from the optical axis position, thearithmetic operation unit 28 also measures the toe angle (step S15A).

More specifically, as shown in FIG. 32, the relationship with respect tothe toe angle θTOE is expressed as:

tan(θTOE)=LPY/LX″

wherein LX″ is the distance between the measuring light irradiatingpoint of the laser displacement gauge 6-1 and the measuring lightirradiating point of the laser displacement gauge 6-2.

Accordingly, the toe angle θTOE is expressed as:

θTOE=tan⁻¹(LPY/LX″)

Here, LPY is |LP1−LP2|, so the toe angle θTOE can be expressed as:

θTOE=tan⁻¹(|LP 1−LP 2|/LX″)

Since the distance X″ between the irradiation points P1 and P2 can belong on the measuring plate of this embodiment, the accuracy inmeasuring the toe angle θTOE can be improved.

As in the first embodiment, the following steps are then carried out:calculating the distance da between the center coordinates CCA of thevisual field ARA and the center coordinates (X0, Z0) of the firstcircular mark MC1 (step S16); calculating the angle θa formed by avirtual line in parallel with the correction line CL extending throughthe center coordinates of the visual field ARA with respect to the lineconnecting the center coordinates of the visual field ARA and the centercoordinates of the first circular mark MC1 (step S17); calculating thedistance Xa and the distance Ya (step SI 8); calculating the position ofthe second circular mark MC2 n closest to the center coordinates of thevisual field ARA by counting the number (nx) of second circular markssituated between the closest second circular mark MC2 n and the firstcircular mark MC1 in the X direction, and the number (ny) of the secondcircular marks in the Z direction (step S19); calculating the distancesXb and Yb between the center coordinates (X0, Z0) of the second circularmark MC2 n closest to the center coordinates of the visual field ARA andthe center coordinates of the first circular mark MC1 (step S20); andcalculating the angle θi(low accuracy) formed by the X-axis of thevisual field ARA and the distance dd (low accuracy) between the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARA and the center coordinates of thevisual field ARA (step S21).

Further steps are carried out as in the first embodiment: calculatingthe low accuracy distances Xi and Yi between the center coordinates ofthe visual field ARA and the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARA(step S22); converting the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARB ofthe color CCD camera 5B into a dot address (IX, IY) (step S23);calculating the angle θb (high accuracy) formed by the X-axis of thevisual field ARA and the distance Db (high accuracy) between the centercoordinates of the visual field ARB and the center coordinates of theclosest second circular mark MC2 n on the visual field ARB of the colorCCD camera 5B (step S24); calculating the high accuracy distances Xc andYc between the center coordinates of the visual field ARB and the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB (step S25); converting the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARBof the color CCD camera SB into a dotaddress (X, Y) (step S26); and transforming the dot address (X, Y) intothe system of coordinates including the X-axis and Z-axis on themeasuring surface 4S of the measuring plate 4, so as to calculate a dotaddress (x, y) in the system of coordinates including the X-axis andZ-axis on the measuring surface 4S (step S27).

The arithmetic operation unit 28 next calculates the caster angle θCASbased on the second inclination data DSL2 outputted from the casterangle measuring inclination gauge SCAS (step S28A), and calculates thecamber angle θCAM based on the first inclination data DSL1 outputtedfrom the camber angle measuring inclination gauge SCAM (step S29A).

As described so far, in the second embodiment, the Y-direction distancefrom the measuring plate can be accurately calculated with the laserdisplacement gauges being secured. As there is no need to employ an X-Ystage or the like for driving the laser displacement gauges, thestructure of the device can be simplified, and manufacturing costs canbe reduced as well.

Although the distance measuring area MLA extends in longitudinaldirection of the measured vehicle 2 with respect to the measuring markarea MRK, it may be situated only one side of the measuring mark areaMRK. In such a case, however, the measurement accuracy becomes lower,because the irradiation points cannot be separated.

C: Third Embodiment

The following is a description of a third embodiment of the presentinvention.

Structure of the Wheel Alignment Measuring Device

FIG. 33 is a block diagram illustrating the structure of the wheelalignment measuring device. Like reference numerals are allotted to likecomponents in FIG. 33 and FIG. 1 of the first embodiment.

The wheel alignment measuring device 1B comprises: a measuring plate 4Bto be attached to a wheel 3 of a measured vehicle 2; a measuring unit 7which picks up the image of the measuring surface 4S of the measuringplate 4 with an image pick-up unit 5 equipped with two CCD camerascapable of picking up color images, and measures the distance from themeasuring surface 4S of the measuring plate with four laser displacementgauges 6-1 to 6-4; and a data processing control unit 8B which performsalignment operations based on output signals from the measuring unit 7,and controls the measuring unit 7.

Structure of the Measuring Plate

FIGS. 34A and 34B show the measuring plate. FIG. 34A is a front view ofthe measuring plate, and FIG. 34B is a side view of the measuring plate.

The measuring surface 4S of the measuring plate 4B is flat, and as shownin FIGS. 34A and 34B, it consists of: a base BB which is colored black;a first circular mark MC1 which is colored red and serves as a referencemark with the origin O of the measuring surface 4S in its center; aplurality of second circular marks MC2 which are colored blue; aplurality of correction lines CL which are colored white; and a distancemeasuring area MLA which is optically uniform (i.e., uniform inreflectance). The plurality of second circular marks MC2 have centercoordinates at the intersections of first parallel virtual lines (onlytwo first virtual lines VL11 and VL12 are shown in FIG. 34A) and secondparallel virtual lines (only two second virtual lines VL21 and VL22 areshown in FIG. 34A). The plurality of correction lines CL are in parallelwith either the first virtual lines or the second virtual lines (theyare in parallel with the second virtual lines VL21 and VL22 in FIG.34A), and their interval distances Δd are uniform. Measuring lightemitted from the laser displacement gauges 6-1 to 6-3 irradiates thedistance measuring area MLA.

As the circular marks MC1 and MC2, and the correction lines CL serve asmeasuring scales, they should be drawn with a certain precision so thatdesired accuracy can be achieved in measurement.

The measuring surface 4S of the measuring plate 4 of this embodiment isthe same as in FIG. 4 of the first embodiment.

Structure of the Measuring Unit

FIG. 35 is a partial perspective view of the measuring unit, FIG. 36 isa side view of the measuring unit, and FIG. 37 is a front view of themeasuring unit.

The measuring unit 7 comprises: a holding plate 10B which is rectangularand holds the four laser displacement gauges 6-1 to 6-4; and the imagepick-up unit 5 which is provided on the rear side of the holding plate10B and picks up images of the measuring plate 4 through an opening10BA.

Structure of the Data Processing Control Unit

FIG. 38 is a block diagram illustrating the structure of the dataprocessing control unit 8B.

The data processing control unit 8B comprises a display 25, a colorseparation circuit 27, and an arithmetic operation unit 28. The display25 displays an image based on first picked-up image data DGG1 outputtedfrom a color CCD camera 5A (mentioned later) or second picked-up imagedata DGG2 outputted from a color CCD camera 5B. The color separationcircuit 27 performs color separation based on the first picked-up imagedata DGG1 and the second picked-up image data DGG2 outputted from theimage pick-up unit 5, and outputs red picked-up image data DRcorresponding to red, green picked-up image data DG corresponding togreen, and blue picked-up image data DB corresponding to blue. Thearithmetic operation unit 28 outputs: X-coordinate data X on themeasuring surface 4S of the measuring plate 4 in a predeterminedposition in a high-resolution picked-up image (for instance, the centerof the picked-up image); Y-coordinate data Y of the measuring surface4S; Z-coordinate data Z on the measuring surface 4S of the measuringplate 4 in a predetermined position in a high-solution picked-up image;an inclination θx with respect to the X-axis on the measuring surface4S; an inclination θy with respect to the Y-axis on the measuringsurface 4S; an inclination θz with respect to the Z-axis on themeasuring surface 4S (these inclination data are used as a basis in spinangle data DSP operations); and position control data DPC, based onoutput signals DLD1 to DLD4 from the four laser displacement gauges 6-1to 6-4, the red picked-up image data DR, the green picked-up image dataDG, and the blue picked-up image data DB.

Here, the red picked-up image data DR include first red picked-up imagedata DR1 corresponding to the first picked-up image data DGG1 and secondred picked-up image data DR2 corresponding to the second picked-up imagedata DGG2, the green picked-up image data DG include first greenpicked-up image data DG1 corresponding to the first picked-up image dataDGG1 and second green picked-up image data DG2 corresponding to thesecond picked-up image data DGG2, and the blue picked-up image data DBinclude first blue picked-up image data DB1 corresponding to the firstpicked-up image data DGG1 and second blue picked-up image data DB2corresponding to the second picked-up image data DGG2.

The structure and arrangement of the image pick-up unit 5 are the sameas in FIGS. 9 to 12 of the first embodiment.

Arrangements of the Laser Displacement Gauges

FIGS. 39 show the arrangements of the laser displacement gauges. FIG.39A is a perspective view illustrating the arrangements of the laserdisplacement gauges, FIG. 39B is a side view of the laser displacementgauges in the initial state, and FIG. 39C is a side view of the laserdisplacement gauges in a measuring state.

As shown in FIGS. 39A and 39B, the laser displacement gauges 6-1 to 6-4in the initial state are arranged so that the measuring laserirradiation points P1 to P4 are situated at the comers of a virtualparallelogram whose diagonal lines cross at the center point of thefirst circular mark MC1.

Here, as shown in FIG. 40, the laser displacement gauges 6-1 to 6-3 aredisposed so that the irradiation points P1 to P3 are situated within thecommon area ARUP (surrounded by a solid line and a dashed line) betweena measuring surface 4SUP corresponding to the measuring plate 4 in thefurthest position in the positive direction of the Z-axis and ameasuring surface 4SREF corresponding to the measuring plate 4 in thereference position (in the initial state). The laser displacement gauges6-2 to 6-4 are arranged so that the irradiation points P2 to P4 aresituated within the common area ARDN (surrounded by a solid line and achain line) between the measuring surface 4SREF and the measuringsurface 4SDN corresponding to the measuring plate 4 in the furthestposition in the negative direction of the Z-axis.

As shown in FIG. 41A, the irradiation points P1 to P4 are situated atthe corners of the virtual parallelogram P1P2P3P4. Assuming theintersection X of the diagonal lines P1P4 and P2P3, the distance LZbetween the intersection X and the irradiation point P1 and the distanceLX between the intersection X and the irradiation point P4 are made aslong as possible so as to improve the accuracy of the camber angle θCAMIn the initial state, the intersection X is made equal to the centerpoint O of the first circular mark MC1.

The arithmetic operation unit 28B judges whether the intersection X isin the positive direction or in the negative direction of the Z-axiswith respect to the center point O of the first circular mark MC1 (seeFIG. 41B). If the intersection X is situated in the position directionof Z-axis with respect to the center point O, the arithmetic operationunit 28B calculates the camber angle θCAM from the output signals DLD1to DLD3 of the laser displacement gauges 6-1 to 6-3 corresponding to theirradiation points P1 to P3. If the intersection X is situated in thenegative direction of the Z-axis with respect to the center point O ofthe first circular mark MC1, the arithmetic operation unit 28Bcalculates the camber angle θCAM from the output signals DLD2 to DLD4 ofthe laser displacement gauges 6-2 to 6-4 corresponding to theirradiation points P2 to P4. To judge whether the intersection X issituated in the positive direction or in the negative direction of theZ-axis with respect to the center point O of the first circular markMC1, the distance from the measuring surface 4S corresponding to theoutput signal DLD1 or the output signal DLD4 is judged as to whether itexceeds the measurable range (i.e., whether one of the laser lights doesnot irradiate the measuring surface 4S), and the optical axis of thecolor CCD camera 5B is judged as to where it is situated on themeasuring surface 4S based on the image processing result of the colorCCD camera 5B.

If the intersection X is situated in the positive direction of theZ-axis with respect to the center point o of the first circular markMC1, the camber angle θCAM is calculated from the output signals DLD1 toDLD3 of the laser displacement gauges 6-1 to 6-3 corresponding to theirradiation points P1 to P3. If the intersection X is situated in thenegative direction of the Z-axis with respect to the center point O ofthe first circular mark MC1, the camber angle θCAM is calculated fromthe output signals DLD2 to DLD4 of the laser displacement gauges 6-2 to6-4 corresponding to the irradiation points P2 to P4.

The number of the laser displacement gauges may be larger than four, aslong as three or more laser irradiation points are secured when themeasuring plate 4 is in the measurement area.

Measuring Operations

The following is a description of measuring operations, with referenceto FIGS. 42 to 44.

Here, the first circular mark MC1 should be always included in an imagepicked up by the color CCD camera 5A that constitutes the image pick-upunit 5, and the measuring plate 4 is attached to the wheel 3 of themeasured vehicle 2 so that the origin O of the measuring surface 4Scorresponds to the rotational center axis of the wheel 3.

FIG. 42 is a flowchart of the measuring operations. Like referencenumerals are allotted to like components in FIG. 42 and FIG. 14 of thefirst embodiment.

As in the first embodiment, the wheel 3 of the measured vehicle 2 isfirst driven upward or downward by an actuator (not shown),independently of other wheels. The actuator is then stopped at the emptyvehicle weight to maintain a stopped state (step S1).

The holding plate 10 and the image pick-up unit 5 are disposed so thatthey face to the measuring surface 4S of the measuring plate 4, and theoptical axes of the color CCD cameras 5A and 5B that constitute theimage pick-up unit 5 are arranged in line with the origin O of themeasuring surface 4S (step S2).

Because of this, the intersection of the laser irradiation points P1 toP4 of the laser displacement gauges 6-1 to 6-4 corresponds to the originO.

As in the first embodiment, the following operations are carried out:picking up an image of the measuring surface 4S of the measuring plate 4by the image pick-up unit 5 (step S3); outputting the first picked-upimage data DGG1 and the second picked-up image data DGG2 (step S4);performing color separation by the color separation circuit 27 (stepS5); detecting the first circular mark MC1 by conducting a rough searchat DN-dot intervals (step S6); detecting the first circular mark MC1 byconducting a fine search with a scan in the positive direction of theX-axis at 1-dot intervals (step S7); calculating the Z-axis centercoordinate Z0 (step S8); detecting the first circular mark MC1 byconducting a rough search at CN-dot intervals with a scan in thepositive direction of the Z-axis (step S9); and detecting the firstcircular mark MC1 by conducting a fine search in the positive directionof the X-axis at 1-dot intervals (equivalent to intervals of L5A/NN mm)until the first circular mark MC1 can no longer be detected, storing thedot number M1(=1 to NN) in the X-axis direction when the first circularmark MC1 is detected for the last time, and conducting a fine search ofthe first circular mark MC1 in the negative direction of the X-axis(step S10).

In step S10, when the first circular mark MC1 becomes undetectableagain, the X-axis center coordinate X0 is calculated based on the dotnumber M2 (=1 to NN) in the X-axis direction at the last detection ofthe first circular mark MC1 (step S11B).

As shown in FIG. 24, the correction lines CL are subjected to samplingbased on the white image obtained by adding the second red picked-upimage data DR2, the second green picked-up image data DG2, and thesecond blue picked-up image data DB2 outputted from the color CCD camera5B, and the inclination θ of the correction lines CL is calculated fromthe positional data by the method of least squares (step S12B).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the center coordinates (X0, Z0) of the first circular mark MC1determined in steps S8 and S11B and the center coordinates CCB of thevisual field ARB of the color CCD camera 5B is calculated (step S13B).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the position of the visualfield ARB can be roughly detected.

While calculating the center coordinates (X0, Z0) of the first circularmark MC1 and the distance LL, the arithmetic operation unit 28 alsocalculates the distance from the first circular mark MC1 on themeasuring surface 4S of the measuring plate 4, based on the outputsignals DLD1 to DLD4 of the laser displacement gauges 6-1 to 6-4.

As in the first embodiment, the following steps are then carried out:calculating the distance da between the center coordinates CCA of thevisual field ARA and the center coordinates (X0, Z0) of the firstcircular mark MC1 (step S16); calculating the angle θ a formed by avirtual line in parallel with the correction line CL extending throughthe center coordinates of the visual field ARA with respect to the lineconnecting the center coordinates of the visual field ARA and the centercoordinates of the first circular mark MC1 (step S17); calculating thedistance Xa and the distance Ya (step S18); calculating the position ofthe second circular mark MC2 n closest to the center coordinates of thevisual field ARA by counting the number (nx) of second circular markssituated between the closest second circular mark MC2 n and the firstcircular mark MC1 in the X direction, and the number (ny) of the secondcircular marks in the Z direction (step S19); calculating the distancesXb and Yb between the center coordinates (X0, Z0) of the second circularmark MC2 n closest to the center coordinates of the visual field ARA andthe center coordinates of the first circular mark MC1 (step S20); andcalculating the angle θi(low accuracy) formed by the X-axis of thevisual field ARA and the distance dd (low accuracy) between the centercoordinates of the visual field ARA and the center coordinates of thesecond circular mark MC2 n closest to the center coordinates of thevisual field ARA (step S21).

Further steps are carried out as in the first embodiment: calculatingthe low accuracy distances Xi and Yi between the center coordinates ofthe visual field ARA and the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARA(step S22); converting the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARB ofthe color CCD camera 5B into a dot address (IX, IY) (step S23);calculating the angle θb (high accuracy) formed by the X-axis of thevisual field ARA and the distance Db (high accuracy) between the centercoordinates of the visual field ARB and the center coordinates of theclosest second circular mark MC2 n on the visual field ARB of the colorCCD camera 5B (step S24); calculating the high accuracy distances Xc andYc between the center coordinates of the visual field ARB and the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB (step S25); converting the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB of the color CCD camera 5B into adot address (X, Y) (step S26); and transforming the dot address (X, Y)into the system of coordinates including the X-axis and Z-axis on themeasuring surface 4S of the measuring plate 4, so as to calculate a dotaddress (x, y) in the system of coordinates including the X-axis andZ-axis on the measuring surface 4S (step S27).

The arithmetic operation unit 28 next calculates the caster angle basedon the inclination of the scale line with respect to the horizontaldirection (or the vertical direction) of the picked-up image (stepS28B).

In this case, at least three irradiation points among the measuringlaser irradiation points P1 to P4 of the laser displacement gauges 6-1to 6-4 are always situated on the measuring surface 4S of the measuringplate 4. Because of that, the output signals DLD1 to DLD4 of the laserdisplacement gauges 6-1 to 6-4 are secure, providing accurate distanceinformation.

Based on the secure output signals DLD1 to DLD4, the camber angle θCAMcan be accurately calculated from the differences in geometric distancefrom the measuring laser irradiation points P1 to P4 on the measuringsurface 4S of the measuring plate 4 corresponding to the laserdisplacement gauges 6-1 to 64, respectively (step S29B).

Calculation of the Camber Angle

The following is a description of the calculation of the camber angleθCAM with reference to FIGS. 43 and 44.

The laser irradiating emitting portions P6-1 to P6-4 of the laserdisplacement gauges 6-1 to 6-4 (the reference numerals P6-1 to P6-4 alsoindicates the position of the emitting portions) are situated on avirtual plane VPL containing a virtual line VL in parallel with thevertical direction of the measured vehicle. The emitting portions P6-1to P6-4 are arranged at the comers of a virtual parallelogram PB whichis located so that the virtual line VL overlaps with the diagonal lineP6-1 P6-4 of the virtual parallelogram PB on the virtual plane VPL.

FIG. 43 shows the measuring plate 4 in the positive direction of theZ-axis. In such a case, the camber angle θCAM is calculated based on theoutput signals DLD1 to DLD3 of the laser displacement gauges 6-1 to 6-3.

More specifically, the distance LP23 from the middle point P23 betweenthe irradiation points P2 and P3 to the intersection PP of the diagonallines of the virtual parallelogram PB is expressed as:

LP 23=(LP 2+LP 3)/2

wherein: LP1 is the distance from the irradiation point P1 correspondingto the output signal DLD1; LP2 is the distance from the irradiationpoint P2 corresponding to the output signal DLD2; and LP3 is thedistance from the irradiation point P3 corresponding to the outputsignal DLD3.

Here, the relationship with the camber angle θCAM can be expressed asshown in FIG. 44:

tan(θcam)=LPX/LZ

Accordingly, the camber angle θCAM can be expressed as:

θCAM=tan⁻¹(LPX/LZ)

Since LPX is expressed as: LPX=|LP1−LP23|, θCAM can also be expressedas:

θCAM=tan⁻¹(|LP 1−LP 23|/LZ)

=tan⁻¹(|LP 1−((LP 2+LP 3)/2)|/LZ)

=tan⁻¹(|(2LP 1−LP 2−LP 3)/2)|·LZ)

As a result, the arithmetic operation unit 28B outputs the dot address xas X-coordinate data DX, the dot address y as Z-coordinate data DZ, andthe camber angle as inclination data DSP and camber angle data DCB.

As described so far, according to the third embodiment, the camber angleθCAM can be accurately calculated with the laser displacement gauges ina fixed state. As there is no need for employing an X-Y stage or thelike for driving the laser displacement gauges, the whole structure canbe simplified, and the manufacturing costs can be lowered.

Based on the picked-up images of the two color CCD cameras 5A and 5B,the position and spin angle corresponding to the center coordinates ofthe first circular mark MC1 on the measuring surface 4S of the measuringplate 4 situated in a predetermined position (in the center in the abovedescription) within the image picked up by the color CCD camera 5B canbe calculated speedily and accurately, which improves reproducibility ofthe measurement.

Thus, wheel alignment measurements can be taken speedily and accurately,while its reproducibility and reliability can be improved as well.

D: Fourth Embodiment

The following is a description of a fourth embodiment of the presentinvention, with reference to the accompanying drawings.

Prior to describing the fourth embodiment in detail, the object of thisembodiment will be given below.

In a conventional optical wheel alignment measuring device of anon-contact type, a measuring unit provided with a plurality of laserdisplacement gauges is disposed on each platform. The measuring unitmoves in the longitudinal direction of the vehicle to optically measurethe distance from a predetermined reference position to the measuringplate attached to one side of the wheel. The position Y, the toe angle,and the camber angle of the measuring plate in the transverse directionare thus calculated. Meanwhile, an image of a predetermined measuringpattern drawn on the measuring surface of the measuring plate is pickedup by a CCD camera, so that the position X of the measuring plate in thelongitudinal direction of the vehicle, the position Z and the casterangle of the measuring plate in the transverse direction can becalculated through image processing.

When measuring the position Y, the toe angle, and the camber angle withthe non-contact type wheel alignment measuring device, the reflectionstrength is varied due to the laser beams emitted onto the measuringpattern on the measuring surface from the laser displacement gauges,which results in an inaccurate displacement measurement.

In order to solve this problem, a laser irradiation area which isoptically uniform (i.e., uniform in reflectance) is formed on themeasuring plate, and an X-Z driving unit is provided. The X-Z drivingunit holds the plurality of laser displacement gauges at intervals, anddrives the holding unit, as in the X-Z stage (see FIG. 23), in the Xdirection and the Z direction on a plane in parallel with a planecontaining the measuring surface of the measuring plate set in thereference position. Here, the laser beams always irradiate the laserirradiation area, following the displacement in the X-Z direction of themeasuring plate.

If the X-Z stage is driven, a stepping motor (a pulse motor) isgenerally used.

Such a stepping motor is used in open-loop control, and the rotationalangle of the stepping motor corresponds to the pulse number. Thus, thetravel distance of the X-Z stage can be specified by the pulse number.Also, since no displacement sensor is required for position return, thestructure of the driving unit can be simplified.

In a general operation state of the X-Z stage, the target control valueis the rest position, and the driving pulse can be given by a constantfrequency, so that the stepping motor is driven at constant rotationspeed.

However, if the X-Z stage is employed in a wheel alignment measuringdevice, the control target becomes the rotational center of the wheel,and the rotational center moves during measurement.

According to a conventional control method, to follow the movement ofthe rotational center, the stepping motor is driven at a rotationalangle several times larger than the smallest rotational angle (0.17°,for instance) corresponding to one pulse of the stepping motor everycorrection time (every 0.1 second, for instance). However, the variationof the target control value in the wheel alignment measurement by theconventional control method is irregular, and the amount of variation istoo large to follow.

As a result, the difference from the target control value graduallybecomes larger to the point where the laser beams emitted from the laserdisplacement gauges no longer irradiate the laser irradiation area,which results in discontinuance of the wheel alignment measurement.

To solve such a problem, the stepping motor should be rotated withlarger steps in the correction time so as to avoid a time lag incontrol.

In such a case, the stepping motor needs to have a large driving forceto obtain a high speed without causing step-out (an uncontrollablestate).

Also, great inertia force is caused due to the step-like movement of theX-Z stage.

The structure containing the X-Z stage is subjected to impact force thatcauses vibration to the whole structure. This hinders accurate wheelalignment measurement.

In the prior art, a DC servomotor or an AC servomotor whose number ofrotation is proportional to the deviation value is employed in place ofa stepping motor so as to prevent vibration of the structure containingthe X-Z stage due to impact force.

In the case where a DC servomotor or an AC servomotor is employed, it isnecessary to perform closed-loop control using an X-direction positionsensor and a Y-direction position sensor for position control of the X-Zstage. This, however, only makes the structure more complicated.

A DC servomotor or an AC servomotor is larger than a stepping motor withthe same power generation. This also causes a problem that the deviceitself becomes larger, and that the complicated structure of aservomotor raises manufacturing costs.

In the conventional optical wheel alignment measuring device describedabove, when measuring the position Y, the toe angle, and the camberangle, the reflection strength is varied due to the laser beams emittedonto the measuring pattern on the measuring surface from the laserdisplacement gauges. This also results in inaccurate displacementmeasurement.

In view of those problems, the object of the fourth embodiment is toprovide a stepping motor control device and a wheel alignment measuringdevice as well as a stepping motor control method and a wheel alignmentmeasuring device, in which a stepping motor can be smoothly controlledat high acceleration without step-out in the wheel alignmentmeasurement, and accurate measurements can be taken with simpler andcompact structures at lower manufacturing costs.

The following is a detailed description of the fourth embodiment.

Structure of the Alignment Measuring Device

FIG. 45 is a block diagram illustrating the structure of the wheelalignment measuring device. Like reference numerals are allotted to likecomponents in FIG. 45 and FIG. 1 of the first embodiment.

The wheel alignment measuring device comprises: a measuring plate 4B tobe attached to a wheel 3 of a measured vehicle (see FIG. 35); ameasuring unit 7 which picks up the image of the measuring surface 4S ofthe measuring plate 4 with an image pick-up unit 5 equipped with two CCDcameras capable of picking up color images, and measures the distancefrom the measuring surface 4S of the measuring plate 4 with three laserdisplacement gauges 6-1 to 6-3; and a data processing control unit 8Cwhich performs alignment operations based on output signals from themeasuring unit 7, and controls the measuring unit 7.

Structure of the Measuring Unit

FIG. 46 is a partial perspective view of the measuring unit, FIG. 47 isa front view of the measuring unit, and FIG. 48 is a side view of themeasuring unit.

The measuring unit 7 comprises: an L-shaped holding plate 10C havingthree laser displacement gauges 6-1 to 6-3; an image pick-up unit 5which is provided on the rear side of the holding plate 10C and picks upimages of the measuring plate 4B from the rear of the holding plate 10C;a Z-axis direction driving unit 12 which drives a Z-axis directionstepping motor 11 to drive the holding plate 10C in the Z-axisdirection; an X-axis driving unit 14 which drives an X-axis directionstepping motor 13 to drive the holding plate 10C in the X-axisdirection; a holding arm 15 which holds the holding plate 10C, the imagepick-up unit 5, the Z-axis direction driving unit 12, and the X-axisdirection driving unit 14, on their rear surfaces; and a base unit 16which secures the holding arm 15 to the ground.

The X-axis direction driving unit 12 comprises: a screw shaft 17 havinga feeding groove; a slider unit 18 which is slidably engaged with thescrew shaft 17 and holds the holding plate 10C; a Z-axis directionmanual driving unit (not shown) having a Z-axis direction driving knobfor manual positioning; and a Z-axis direction control unit 12A (shownin FIG. 49) for controlling the entire Z-axis direction driving unit 12.

The X-axis direction driving unit 14 comprises: a screw shaft 19 havinga feeding groove; a slider unit 20 which is slidably engaged with thescrew shaft 19 and holds the holding arm 15; and an X-axis directioncontrol unit 14A (shown in FIG. 50) for controlling the entire X-axisdirection driving unit 14.

The measuring unit 7 further comprises a Y-axis direction manual drivingunit (not shown) having a Y-axis direction driving knob for manualpositioning in the Y-axis direction.

The measuring unit 7 also has a body sensor (not shown) for detectingthe position and inclination of the body of the measured vehicle 2. Thebody sensor mechanically detects the position of the detection point BP(shown in FIG. 46), which varies when the platform PH is driven upwardand downward by a power applying head 9, to detect the position andinclination of the body of the measured vehicle 2. Based on the detecteddata, the data processing control unit 8 performs measurement datacorrection.

Structure of the Z-axis (X-axis) Direction Control Unit

Referring now to FIGS. 49 to 54, the structure of the Z-axis (X-axis)direction control unit will be described. The following descriptionconcerns only the Z-axis direction control unit 12A, for the Z-axisdirection control unit 12A and the X-axis direction control unit 14Ahave the same structure.

The Z-axis direction control unit 12A comprises a deviation calculatingunit 30, a numeral-frequency conversion unit 31, and a position countunit 32. Control target numerical data N0, which are control targetnumeric values, are inputted into one input terminal, control resultnumerical data Ni corresponding to the real position of the controlresult are then inputted, and the deviation calculating unit 30 outputsthe deviation as deviation numerical data ΔN. The numeral-frequencyconversion unit 31 converts the deviation numerical data ΔN and thenoutputs a forward driving pulse signal CW and a reverse driving pulsesignal CCW. The position count unit 32 counts up and down based oneither the forward driving pulse signal CW or the reverse driving pulsesignal CCW, and then outputs the control result numerical data Ni.

Based on the control target numerical data N0 and the control resultnumerical data Ni, the deviation numerical data ΔN is expressed by anequation:

ΔN=|Ni−N 0|

The deviation ΔN is made proportional to the forward driving pulsesignal CW and the reverse driving pulse signal CCW outputted from thenumeral-frequency conversion unit 31, as shown in FIG. 51. In the caseof Ni−N0≧0, the numeral-frequency conversion unit 31 outputs the forwarddriving pulse signal CW. In the case of Ni−N0<0, the numeral-frequencyconversion unit 31 outputs the reverse driving pulse signal CCW.

Next, the operation of the X-axis direction control unit will bedescribed.

The control target numerical data N0 (actually corresponding to theposition of the first circular mark MC1) are inputted from the outside,and the control result numerical data Ni are inputted from the positioncount unit 32. The deviation is then outputted as the deviationnumerical data ΔN to the numeral-frequency conversion unit 31.

Based on the relationship shown in FIG. 51, the numeral-frequencyconversion unit numeral-frequency converts the deviation numerical dataΔN to output the forward driving pulse signal CW and the reverse drivingpulse signal CCW to the Z-axis direction stepping motor 11.

By doing so, the Z-axis direction stepping motor 11 rotates the screwshaft 17 to drive the holding plate 10C to a predetermined position.

At the same time of driving the holding plate 10C, the position countunit 32 counts up based on either the pulse number of the forwarddriving pulse signal CW or the pulse number of the reverse driving pulsesignal CCW, and counts down based on the other. The position count unit32 then outputs the control results numerical data Ni as positioninformation to the deviation calculating unit 30, thereby forming afeedback loop to perform accurate position control.

Structure of the Data Processing Control Unit

FIG. 52 is a block diagram illustrating the structure of the dataprocessing control unit 8C.

The data processing control unit 8C comprises a display 25, an X-Zstepping motor control unit 26, a color separation circuit 27, and anarithmetic operation unit 28C. The display 25 displays an image based onthe first picked-up image data DGG1 outputted from the color CCD camera5A or the second picked-up image data DGG2 outputted from the color CCDcamera 5B. The X-Z stepping motor control unit 26 controls the drivingof the Z-axis stepping motor 11 and the X-axis stepping motor 14, basedon position control data DPC. The color separation circuit 27 performscolor separation based on the first picked-up image data DGG1 and thesecond picked-up image data DGG2 outputted from the image pick-up unit5, and outputs red picked-up image data DR corresponding to red, greenpicked-up image data DG corresponding to green, and blue picked-up imagedata DB corresponding to blue. The arithmetic operation unit 28Coutputs: X-coordinate data X on the measuring surface 4S of themeasuring plate 4 in a predetermined position in a high-resolutionpicked-up image (for instance, the center of the picked-up image);Y-coordinate data Y of the measuring surface 4S; Z-coordinate data Z onthe measuring surface 4S of the measuring plate 4 in a predeterminedposition in a high-solution picked-up image; an inclination θx withrespect to the X-axis on the measuring surface 4S; an inclination θywith respect to the Y-axis on the measuring surface 4S; an inclinationθz with respect to the Z-axis on the measuring surface 4S (theseinclination data are used as a basis in spin angle data DSP operations);and the position control data DPC, based on output signals DLD1 to DLD3from the three laser displacement gauges 6-1 to 6-3, the red picked-upimage data DR, the green picked-up image data DG, and the blue picked-upimage data DB.

Here, the red picked-up image data DR include first red picked-up imagedata DR1 corresponding to the first picked-up image data DGG1 and secondred picked-up image data DR2 corresponding to the second picked-up imagedata DGG2, the green picked-up image data DG include first greenpicked-up image data DG1 corresponding to the first picked-up image dataDGG1 and second green picked-up image data DG2 corresponding to thesecond picked-up image data DGG2, and the blue picked-up image data DBinclude first blue picked-up image data DB1 corresponding to the firstpicked-up image data DGG1 and second blue picked-up image data DB2corresponding to the second picked-up image data DGG2.

The structure and arrangement of the image pick-up unit 5 are the sameas in FIGS. 9 to 12 of the first embodiment.

Arrangements of the Laser Displacement Gauges

FIG. 53 show the arrangements of the laser displacement gauges. FIG. 53Ais a perspective view illustrating the arrangements of the laserdisplacement gauges, FIG. 53B is a side view of the laser displacementgauges in the initial state, and FIG. 53C is a side view of the laserdisplacement gauges in a measuring state.

As shown in FIGS. 53A and 53B, the laser displacement gauges 6-1 to 6-3in the initial state are arranged so that the measuring laserirradiation points P1 to P3 are situated within the distance measuringarea MLA.

As described later, servo control is performed by an amountcorresponding to the amount of displacement in the X direction (or afirst direction) and the Z direction (or a second direction) of thefirst circular mark MC1 on the measuring surface 4S of the measuringplate 4B, based on the first picked-up image data DGG1 and the secondpicked-up image data DGG2 outputted from the image pick-up unit 5. TheZ-axis direction stepping motor 11 of the Z-axis direction driving unit12 is driven so as to drive the holding plate 10C in the Z-axisdirection, while the X-axis direction stepping motor 13 of the X-axisdirection driving unit 14 is driven so as to drive the holding plate 10Cin the X-axis direction. Even if the measuring surface 4S is inclinedduring measurement as shown in FIG. 53C, the measuring laser irradiationpoints P1 to P3 of the laser displacement gauges 6-1 to 6-3 are situatedwithin the distance measuring area MLA, regardless of the position ofthe optical axis of the color CCD camera 5B.

The number of the laser displacement gauges may be more than three.

Measuring Operations

The following is a description of the measuring operations.

Here, the first circular mark MC1 should be always included in an imagepicked up by the color CCD camera 5A that constitutes the image pick-upunit 5, and the measuring plate 4B is attached to the wheel 3 of themeasured vehicle 2 so that the origin O of the measuring surface 4Scorresponds to the rotational center axis of the wheel 3.

FIG. 54 is a flowchart of the measuring operations. Like referencenumerals are allotted to like components in FIG. 54 and FIG. 14 of thefirst embodiment.

As in the first embodiment, the wheel 3 of the measured vehicle 2 isfirst driven upward or downward by an actuator (not shown),independently of other wheels. The actuator is then stopped at the emptyvehicle weight to maintain a stopped state (step S1).

The holding plate 10C and the image pick-up unit 5 are driven in theZ-axis direction by hand or by actuating the Z-axis direction drivingunit 12 and the X-axis direction driving unit 14 so that they face tothe measuring surface 4S of the measuring plate 4, the optical axes ofthe color CCD cameras 5A and 5B that constitute the image pick-up unit 5are arranged in line with the origin O of the measuring surface 4S, andthe measuring laser irradiation points P1 to P3 (see FIG. 53A) of thelaser displacement gauges 6-1 to 6-3 are set within the distancemeasuring area MLA (step S2C).

As in the first embodiment, the following operations are carried out:picking up an image of the measuring surface 4S of the measuring plate 4by the image pick-up unit 5 (step S3); outputting the first picked-upimage data DGG1 and the second picked-up image data DGG2 (step S4);performing color separation by the color separation circuit 27 (stepS5); detecting the first circular mark MC1 by conducting a rough searchat DN-dot intervals (step S6); detecting the first circular mark MC1 byconducting a fine search with a scan in the positive direction of theX-axis at 1-dot intervals (step S7); calculating the Z-axis centercoordinate Z0 (step S8); detecting the first circular mark MC1 byconducting a rough search at CN-dot intervals with a scan in thepositive direction of the Z-axis (step S9); and detecting the firstcircular mark MC1 by conducting a fine search in the positive directionof the X-axis at 1-dot intervals (equivalent to intervals of L5A/NN mm)until the first circular mark MC1 can no longer be detected, storing thedot number M1 (=1 to NN) in the X-axis direction when the first circularmark MC1 is detected for the last time, and conducting a fine search ofthe first circular mark MC1 in the negative direction of the X-axis(step S10).

In step S10, when the first circular mark MC1 becomes undetectableagain, the X-axis center coordinate X0 is calculated based on the dotnumber M2 (=1 to NN) in the X-axis direction at the last detection ofthe first circular mark MC1 (step S11B).

As shown in FIG. 24 of the first embodiment, the correction lines CL aresubjected to sampling based on a white image obtained by adding thesecond red picked-up image data DR2, the second green picked-up imagedata DG2, and the second blue picked-up image data DB2 outputted fromthe color CCD camera 5B, and the inclination θ of the correction linesCL is calculated from the positional data by the method of least squares(step S12B).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the center coordinates (X0, Z0) of the first circular mark MC1determined in steps S8 and S11B and the center coordinates CCB of thevisual field ARB of the color CCD camera 5B is calculated (step S13B).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the position of the visualfield ARB can be roughly detected.

While calculating the center coordinates (X0, Z0) of the first circularmark MC1 and the distance LL, the arithmetic operation unit 28C alsocalculates the distance from the first circular mark MC1 on themeasuring surface 4S of the measuring plate 4, based on the outputsignals DLD1 to DLD3 of the laser displacement gauges 6-1 to 6-3.

The distance LL is then converted into the amount of displacement(travel distance) of the first circular mark MC1 on the measuringsurface 4S. To cancel the amount of displacement, the Z-axis directionstepping motor 11 of the Z-axis direction driving unit 12 and the X-axisdirection stepping motor 13 of the X-axis direction driving unit 14 aredriven so as to drive the holding plate 10C in the X-axis direction andthe Z-axis direction following the track of the first circular mark MC1.Even if the measuring surface 4S is inclined during measurement as shownin FIG. 53C, the measuring laser irradiation points P1 to P3 of thelaser displacement gauges 6-1 to 6-3 are situated within the distancemeasuring area MLA, regardless of the position of the optical axis ofthe color CCD camera 5B.

As a result, the measuring laser irradiation points P1 to P3 of thelaser displacement gauges 6-1 to 6-3 are always situated within thedistance measuring area MLA, so that a position Y as displacementinformation in the Y direction can be surely obtained, and that highlyreliable wheel alignment measurements can be taken in the Y direction aswell.

While calculating the center coordinates (X0, Z0) of the first circularmark MC1 and the distance LL, the arithmetic operation circuit 28C alsocalculates the distance from the first circular mark MC1 on themeasuring surface 4S of the measuring plate 4, based on the outputsignals DLD1 to DLD3 from the laser displacement gauges 6-1 to 6-4.

As in the first embodiment, the following steps are then carried out:calculating the distance da between the center coordinates CCA of thevisual field ARA and the center coordinates (X0, Z0) of the firstcircular mark MC1 (step S16); calculating the angle θa formed by avirtual line in parallel with the correction line CL extending throughthe center coordinates of the visual field ARA with respect to the lineconnecting the center coordinates of the visual field ARA and the centercoordinates of the first circular mark MC1 (step S17); calculating thedistance Xa and the distance Ya (step S18); calculating the position ofthe second circular mark MC2 n closest to the center coordinates of thevisual field ARA by counting the number (nx) of second circular markssituated between the closest second circular mark MC2 n and the firstcircular mark MC1 in the X direction, and the number (ny) of the secondcircular marks in the Z direction (step S19); calculating the distancesXb and Yb between the center coordinates (X0, Z0) of the second circularmark MC2 n closest to the center coordinates of the visual field ARA andthe center coordinates of the first circular mark MC1 (step S20); andcalculating the angle θi (low accuracy) formed by the X-axis of thevisual field ARA and the distance dd (low accuracy) between the centercoordinates of the visual field ARA and the center coordinates of thesecond circular mark MC2 n closest to the center coordinates of thevisual field ARA (step S21).

Further steps are carried out as in the first embodiment: calculatingthe low accuracy distances Xi and Yi between the center coordinates ofthe visual field ARA and the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARA(step S22); converting the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARB ofthe color CCD camera 5B into a dot address (IX, IY) (step S23);calculating the angle θb (high accuracy) formed by the X-axis of thevisual field ARA and the distance Db (high accuracy) between the centercoordinates of the visual field ARB and the center coordinates of theclosest second circular mark MC2 n in the visual field ARB of the colorCCD camera 5B (step S24); calculating the high accuracy distances Xc andYc between the center coordinates of the visual field ARB and the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB (step S25); converting the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB of the color CCD camera 5B into adot address (X, Y) (step S26); and transforming the dot address (X, Y)into the system of coordinates including the X-axis and Z-axis on themeasuring surface 4S of the measuring plate 4, so as to calculate a dotaddress (x, y) in the system of coordinates including the X-axis andZ-axis on the measuring surface 4S (step S27).

The arithmetic operation unit 28C next calculates the caster angle basedon the inclination of the scale line with respect to the horizontaldirection (or the vertical direction) of the picked-up image (stepS28C).

Based on the center coordinates (X0, Z0) of the first circular mark MC1,the Z-axis direction stepping motor 11 of the Z-axis direction drivingunit 12 and the X-axis direction stepping motor 13 of the X-axisdirection driving unit 14 are subjected to servo control, so that theholding plate 10C follows the track of the center of the first circularmark MC1.

The following is a detailed description of the control operation of theZ-axis direction stepping motor 11.

The control target numerical data N0 corresponding to the centercoordinates (X0, Z0) of the first circular mark MC1 are inputted, andthe control result numerical data Ni corresponding to the real positionof the first circular mark MC1 are inputted from the position count unit32. The deviation calculating unit 30 then outputs the deviation as thedeviation numerical data ΔN to the numeral-frequency conversion unit 31.

The numeral-frequency conversion unit 31 converts the deviationnumerical data ΔN based on the relationship shown in FIG. 51.

If Ni−N0≧0, the forward driving pulse signal CW having the obtainedpulse frequency is outputted to the Z-axis direction stepping motor 11.

If Ni−N0<0, the reverse driving pulse signal CCW having the obtainedpulse frequency is outputted to the Z-axis direction stepping motor 11.

The Z-axis direction stepping motor 11 then rotates the screw shaft 17,so that the holding plate 10C follows the track of the centercoordinates (X0, Z0) of the first circular mark MC1.

At the same time of the driving of the holding plate 10C, the positioncount unit 32 counts up based on either the pulse number of the forwarddriving pulse signal CW or the pulse number of the reverse driving pulsesignal CCW, and counts down based on the other, so as to output thecontrol result numerical data Ni as position information to thedeviation calculating unit 30. As a result of this, a feedback loop isformed to realize accurate position control to follow the centercoordinates (X0, Z0) of the first circular mark MC1.

As for the X-axis direction stepping motor 14, the same controloperation is performed.

In this case, the larger the value of |Ni−N0|, the higher the convergingspeed. However, as it nears the control target value, the speed reduces,and eventually, the Z-axis direction stepping motor 11 and the X-axisdirection stepping motor 14 are driven at the limiting resolving angle.Thus, accurate measurements can be taken without causing greatacceleration force and vibration to the holding plate 10C.

The stepping motors are used in a step-out prevented area (a pull-inarea), so that the pulse numbers accurately correspond to the positions,i.e., the control result numerical data Ni accurately correspond to thepositions. Here, no hardware position sensor such as a pulse encoder isnecessary.

As a result, the measuring laser irradiation points P1 to P3 of thelaser displacement gauges 6-1 to 6-3 are always situated within thedistance measuring area MLA. Because of that, the output signals DLD1 toDLD3 of the laser displacement gauges 6-1 to 6-3 become secure,providing accurate distance information.

Based on the secure output signals DLD1 to DLD3, the camber angle θCAMcan be accurately calculated from the differences in geometric distancefrom the measuring laser irradiation points P1 to P3 on the measuringsurface 4S of the measuring plate 4 corresponding to the laserdisplacement gauges 6-1 to 6-3, respectively (step S29C).

The arithmetic operation unit 28C then outputs the obtained dot addressx as X-coordinate data DX, the obtained dot address y as Z-coordinatedata DZ, the obtained spin angle as inclination data DSP, and theobtained camber angle as camber angle data DCB.

As described so far, according to the fourth embodiment, the steppingmotors 11 and 14 are driven without causing large acceleration force sothat the laser displacement gauges 6-1 to 6-3 follow the displacement ofthe center coordinates of the first circular mark MC1, which is thereference mark. The output signals DLD1 to DLD3 of the laserdisplacement gauges 6-1 to 6-3 are obtained in a driven state in such adirection as to cancel the displacement, and because of this, thedisplacement in the Y direction (more specifically, the position Y andthe camber angle) can be calculated speedily and accurately.

Based on picked-up images of the two color CCD cameras 5A and 5B, theposition and the spin angle corresponding to the center coordinates ofthe first circular mark MC1 on the measuring surface 4S of the measuringplate situated in a predetermined position (in the center in the aboveexample) within the image picked up by the color CCD camera 5B can becalculated speedily and accurately. Thus, reproducibility of themeasurement is improved.

As described above so far, according to this embodiment, the wheelalignment can be measured speedily and accurately, and itsreproducibility and reliability can be improved in the fourthembodiment.

Although the position count unit 32 is employed to count up and down theforward driving pulse signal CW and the reverse driving pulse signal CCWin the above embodiment, it may be replaced with a first count unit forcounting the pulse number of the forward driving pulse signal CW, asecond count unit for counting the pulse number of the reverse drivingpulse signal CCW, and a subtraction unit for determining the differencebetween the counts of the first count unit and the second count unit,and outputting the difference as the control result numerical data Ni.

Modifications of the Fourth Embodiment

(a) First Modification

A preferred embodiment of the first modification is a pulse motorcontrol device which controls an external pulse motor for driving adevice to be controlled based on a forward driving pulse signal and areverse driving pulse signal. The pulse motor control device comprises:a deviation calculating unit which compares control target data inputtedfrom the outside with control result data, and outputs deviation data; asignal conversion unit which outputs a forward driving pulse signal or areverse driving pulse signal based on the value of the deviation data; apulse count unit which counts up based on either the pulse number of theforward driving pulse signal or the pulse number of the reverse drivingpulse signal, counts down based on the other, and outputs count databased on the count results; and a control result data generating unitwhich generates and outputs the control result data based on the countdata.

In this modification, the deviation calculating unit compares thecontrol target data inputted from the outside with the control resultdata, and then outputs the deviation data to the signal conversion unit.

The signal conversion unit outputs a forward driving pulse signal or areverse driving pulse signal to the pulse motor based on the deviationdata, and the pulse motor drives the device to be controlled based onthe forward driving pulse signal or the reverse driving pulse signalhaving a pulse number corresponding to the deviation data.

At the same time of those operations, the pulse count unit counts upbased on either the pulse number of the forward driving pulse signal orthe pulse number of the reverse driving pulse signal, and counts downbased on the other. According to the count results, the pulse count unitoutputs the count data to the control result data generating unit. Thecontrol result data generating unit generates the control result databased on the count data, and outputs the data to the deviationcalculating unit. The pulse motor is thus driven at a pulse numberproportional to the deviation amount corresponding to the deviationdata, so that it constantly changes in speed. As a result, no greatacceleration force is applied to the controlled device, and vibrationwhich might be caused due to great acceleration force can be repressed.Thus, a smooth control operation can be performed.

(b) Second Modification

A preferred embodiment of the second modification is a pulse motorcontrol device which controls an external pulse motor for driving adevice to be controlled based on a forward driving pulse signal and areverse driving pulse signal. The pulse motor control device comprises:a deviation calculating unit which compares control result data withcontrol target data inputted from the outside, and outputs deviationdata; a signal conversion unit which outputs a forward driving pulsesignal or a reverse driving pulse signal based on the value of thedeviation data; a pulse count unit which counts the pulse numbers of theforward driving pulse signal and the reverse driving pulse signal; and acontrol result data generating unit which generates and outputs thecontrol result data based on the difference between the forward pulsenumber of the forward driving pulse signal and the reverse pulse numberof the reverse driving pulse signal.

In this modification, the deviation calculating unit compares thecontrol result data with the control target data inputted from theoutside, and then outputs the deviation data to the signal conversionunit.

The signal conversion unit outputs a forward driving pulse signal or areverse driving pulse signal to the pulse motor based on the value ofdeviation data, and the pulse motor drives the device to be controlledbased on the forward driving pulse signal or the reverse driving pulsesignal having a pulse number corresponding to the deviation data.

At the same time of those operations, the pulse count unit counts thepulse numbers of the forward driving pulse signal and the reversedriving pulse signal. The control result data generating unit thengenerates the control result data based on the difference between theforward pulse number of the forward driving pulse signal and the reversepulse number of the reverse driving pulse signal, and outputs the datato the deviation calculating unit. The pulse motor is thus driven at apulse number proportional to the deviation amount corresponding to thedeviation data, so that it constantly changes in speed. As a result, nogreat acceleration force is applied to the controlled device, andvibrations which might be caused due to great acceleration force can berepressed. Thus, a smooth control operation can be performed.

(c) Third Modification

A preferred embodiment of the third modification includes: a measuringplate attached to a wheel of a vehicle; a vertical directiondisplacement detection unit which detects the amount of displacement ofthe reference mark on the measuring surface of the measuring plate in adirection perpendicular to the displacement detecting direction, andoutputs vertical direction displacement detection data; a plurality ofdistance measuring units which measure the distance from the measuringplate by irradiating measuring light onto the measuring plate, andoutput distance measurement data; a holding unit which holds theplurality of distance measuring units at predetermined intervals; adriving unit which is provided with at least two pulse motors fordriving the holding unit in directions perpendicular to each other, anddrives the holding unit in a direction perpendicular to the displacementdetecting direction; and a driving control unit which is provided with apulse motor control unit of the first modification, and controls thedriving unit to drive the holding unit in such a direction as to cancelthe amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, based on thevertical direction displacement detection data.

In this modification, the vertical direction displacement detection unitdetects the amount of displacement in a direction perpendicular to thedisplacement detecting direction of the reference mark on the measuringsurface of the measuring plate attached to a wheel of the vehicle beingmeasured, and outputs the vertical direction displacement data to thedriving control unit. The distance measuring units irradiate measuringlight onto the measuring plate to measure the distance from themeasuring plate, and then outputs the distance measurement data.

At the same time of those operations, the holding unit holds thedistance measuring units at predetermined intervals, and the pulse motorcontrol device of the driving control unit controls the driving unit todrive the holding unit in such a direction as to cancel the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction, based on the vertical directiondisplacement detection data. Since the driving unit drives the holdingunit, as well as the distance measuring units, by at least two pulsemotors in directions perpendicular to each other and to the displacementdetecting direction, the holding unit is driven at constantly variedspeed without causing great acceleration force and unwanted vibration.Thus, the distance measuring units can steadily make an accuratedistance measurement.

(d) Fourth Modification

A preferred embodiment of the fourth modification includes: a measuringplate attached to a wheel of a vehicle; a vertical directiondisplacement detection unit which detects the amount of displacement ofthe reference mark on the measuring surface of the measuring plate in adirection perpendicular to the displacement detecting direction, andoutputs vertical direction displacement detection data; a plurality ofdistance measuring units which measure the distance from the measuringplate by irradiating measuring light onto the measuring plate, andoutput distance measurement data; a holding unit which holds theplurality of distance measuring units at predetermined intervals; adriving unit which is provided with at least two pulse motors fordriving the holding unit in directions perpendicular to each other, anddrives the holding unit in a direction perpendicular to the displacementdetecting direction; and a driving control unit which is provided with apulse motor control unit of the second modification, and controls thedriving unit to drive the holding unit in such a direction as to cancelthe amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, based on thevertical direction displacement detection data.

In this modification, the vertical direction displacement detection unitdetects the amount of displacement in a direction perpendicular to thedisplacement detecting direction of the reference mark on the measuringsurface of the measuring plate attached to a wheel of the vehicle beingmeasured, and outputs the vertical direction displacement data to thedriving control unit. The distance measuring units irradiate measuringlight onto the measuring plate to measure the distance from themeasuring plate, and then outputs the distance measurement data.

At the same time of those operations, the holding unit holds thedistance measuring units at predetermined intervals, and the pulse motorcontrol device of the driving control unit controls the driving unit todrive the holding unit in such a direction as to cancel the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction, based on the vertical directiondisplacement detection data. Since the driving unit drives the holdingunit, as well as the distance measuring units, by at least two pulsemotors in directions perpendicular to each other and to the displacementdetecting direction, the holding unit is driven at constantly variedspeed without causing great acceleration force and unwanted vibration.Thus, the distance measuring units can steadily make an accuratedistance measurement.

(e) Fifth Modification

A preferred embodiment of the fifth modification is the same as thepreferred embodiment of the third modification, except that the verticaldirection displacement detection unit comprises: an image pick-up unitwhich picks up images of the measuring plate to output picked-up imagedata; and a displacement calculating unit which calculates the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction by extracting the image datacorresponding to the reference mark from the picked-up image data, andthen outputs the vertical direction displacement detection data.

In this modification, the image pick-up unit of the vertical directiondisplacement detection unit picks up images of the measuring plate tooutput the picked-up image data to the displacement calculating unit.The displacement calculating unit extracts the image data correspondingto the reference mark from the picked-up image data to calculate theamount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, and then outputsthe vertical direction displacement detection data to the drivingcontrol unit. Thus, the amount of displacement can be speedilycalculated by non-contact image processing, and control operations whichprovide excellent following ability can be performed.

(f) Sixth Modification

A preferred embodiment of the sixth modification is the same as thepreferred embodiment of the fourth modification, except that thevertical direction displacement detection unit comprises: an imagepick-up unit which picks up images of the measuring plate to outputpicked-up image data; and a displacement calculating unit whichcalculates the amount of displacement of the reference mark in adirection perpendicular to the displacement detecting direction byextracting the image data corresponding to the reference mark from thepicked-up image data, and then outputs the vertical directiondisplacement detection data.

In this modification, the image pick-up unit of the vertical directiondisplacement detection unit picks up images of the measuring plate tooutput the picked-up image data to the displacement calculating unit.The displacement calculating unit extracts the image data correspondingto the reference mark from the picked-up image data to calculate theamount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, and then outputsthe vertical direction displacement detection data to the drivingcontrol unit. Thus, the amount of displacement can be speedilycalculated by non-contact image processing, and control operations whichprovide excellent following ability can be performed.

(g) Seventh Modification

A preferred embodiment of the seventh modification is a pulse motorcontrol method for controlling an external pulse motor which drives adevice to be controlled based on a forward driving pulse signal and areverse driving pulse signal. The pulse motor control method comprises:a deviation calculating step of calculating the deviation by comparingthe control target with real control results; a signal generating stepof generating a forward driving pulse signal and a reverse driving pulsesignal based on the deviation; a pulse count step of counting up basedon either the pulse number of the forward driving pulse signal or thepulse number of the reverse driving pulse signal, and counting downbased on the other; and a control result calculating step of outputtingthe control results based on the count results obtained in the pulsecount step.

According to this modification, the real control results are comparedwith the control target so as to calculate the deviation in thedeviation calculating step; a forward driving pulse signal and a reversedriving pulse signal are generated based on the obtained deviation inthe signal generating step; and the external pulse motor drives thedevice being controlled based on the forward driving pulse signal or thereverse driving pulse signal having a pulse number corresponding to thedeviation.

At the same time of those operations, the pulse count unit counts upbased on either the pulse number of the forward driving pulse signal orthe pulse number of the reverse driving pulse signal, and counts downbased on the other in the pulse count step; and control results areobtained based on the count results of the pulse count step. The pulsemotor is thus driven at a pulse number proportional to the deviationamount corresponding to the deviation data, so that it constantlychanges in speed. As a result, no great acceleration force is applied tothe controlled device, and vibration which might be caused due to greatacceleration force can be repressed. Thus, a smooth control operationcan be performed.

(h) Eighth Modification

A preferred embodiment of the eighth modification is a pulse motorcontrol method for controlling an external pulse motor which drives adevice to be controlled based on a forward driving pulse signal and areverse driving pulse signal. The pulse motor control method comprises:a deviation calculating step of calculating the deviation by comparingthe control target with real control results; a signal generating stepof generating a forward driving pulse signal and a reverse driving pulsesignal based on the obtained deviation; a pulse count step of countingup based on either the pulse number of the forward driving pulse signalor the pulse number of the reverse driving pulse signal, and countingdown based on the other; and a control result calculating step ofoutputting the control results based on the difference between theforward pulse number of the forward driving pulse signal and the reversepulse number of the reverse driving pulse signal.

According to this modification, the real control results are comparedwith the control target so as to calculate the deviation in thedeviation calculating step; a forward driving pulse signal and a reversedriving pulse signal are generated based on the obtained deviation inthe signal generating step; and the external pulse motor drives thedevice being controlled based on the forward driving pulse signal or thereverse driving pulse signal having a pulse number corresponding to thedeviation.

At the same time of those operations, the pulse count unit counts thepulse numbers of the forward driving pulse signal and the reversedriving pulse signal, and control results are obtained based on thedifference between the forward pulse number of the forward driving pulsesignal and the reverse pulse number of the reverse driving pulse signal.The pulse motor is thus driven at a pulse number proportional to thedeviation amount corresponding to the deviation data, so that itconstantly changes in speed. As a result, no great acceleration force isapplied to the controlled device, and vibration which might be causeddue to great acceleration force can be repressed. Thus, a smooth controloperation can be performed.

(i) Ninth Modification

A preferred embodiment of the ninth embodiment is a wheel alignmentmeasuring method which utilizes a wheel alignment measuring devicecomprising: a measuring plate attached to a wheel of the vehicle; aplurality of distance measuring units held by a holding member atpredetermined intervals; and a driving unit which is provided with atleast two pulse motor for driving the holding member, and drives theholding member in a direction perpendicular to the displacementdetecting direction. The wheel alignment measuring method comprises: avertical direction displacement detecting step of detecting the amountof displacement of the reference mark on the measuring surface of themeasuring plate in a direction perpendicular to the displacementdetecting direction; a distance measuring step of measuring the distancefrom the measuring plate by irradiating measuring light onto severalspots on the measuring plate; and a driving control step of controllingthe pulse motors to drive the holding member in such a direction as tocancel the amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, based on theamount of displacement in the direction perpendicular to thedisplacement detecting direction, by the pulse motor control method ofthe preferred embodiment of the fifth modification.

According to this modification, the amount of displacement of thereference mark on the measuring surface of the measuring plate in adirection perpendicular to the displacement detecting direction in thevertical direction displacement detecting step; the distance from themeasuring plate is measured by irradiating measuring light onto severalspots on the measuring plate in the distance measuring step; and thepulse motors are controlled to drive the holding member in such adirection as to cancel the amount of displacement of the reference markin a direction perpendicular to the displacement detecting direction,based on the amount of displacement in the direction perpendicular tothe displacement detecting direction, by the pulse motor control methodof the preferred embodiment of the fifth modification in the drivingcontrol step. The holding member is thus driven so that it constantlychanges in speed, and no great acceleration force is applied to thecontrolled device, preventing unwanted vibration. Thus, an accuratedistance measurement can be surely made in the distance measuring step.

(j) Tenth Modification

A preferred embodiment of the tenth modification is a wheel alignmentmeasuring method which utilizes a wheel alignment measuring devicecomprising: a measuring plate attached to a wheel of the vehicle; aplurality of distance measuring units which irradiate measuring lightonto the measuring plate, and are held by a holding member atpredetermined intervals; and a driving unit which is provided with atleast two pulse motors for driving the holding member, and drives theholding member in a direction perpendicular to the displacementdetecting direction. The wheel alignment measuring method comprises: avertical direction displacement detecting step of detecting the amountof displacement of the reference mark on the measuring surface of themeasuring plate in a direction perpendicular to the displacementdetecting direction; a distance measuring step of measuring the distancefrom the measuring plate by irradiating measuring light upon severalspots on the measuring plate; and a driving control step of controllingthe pulse motors to drive the holding member in such a direction as tocancel the amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, based on theamount of displacement of the reference mark on the measuring surface ofthe measuring plate in the direction perpendicular to the displacementdetecting direction, by the pulse motor control method of the preferredembodiment of the sixth modification.

According to the modification, the amount of displacement of thereference mark on the measuring surface of the measuring plate in adirection perpendicular to the displacement detecting direction isdetected in the vertical direction displacement detecting step; thedistance from the measuring plate is measured by irradiating measuringlight upon several spots on the measuring plate in the distancemeasuring step; and the pulse motors are controlled to drive the holdingmember in such a direction as to cancel the amount of displacement ofthe reference mark in the direction perpendicular to the displacementdetecting direction, based on the amount of displacement in thedirection perpendicular to the displacement detecting direction, by thepulse motor control method of the preferred embodiment of the sixthmodification. The holding member is thus driven so that it constantlychanges in speed, and no great acceleration force is applied, whichprevents occurrence of vibration. Thus, an accurate distance measurementcan be surely made in the distance measuring step.

(k) Eleventh Modification

A preferred embodiment of the eleventh modification is a method of theninth modification, in which the vertical direction displacementdetecting step comprises; an image pick-up step of picking up images ofthe measuring plate; and a displacement calculating step of calculatingthe amount of displacement of the reference mark in the directionperpendicular to the displacement detecting direction by extracting animage corresponding to the reference mark from the picked-up images.

According to the modification, images of the measuring plate are pickedup in the image pick-up step, and the image corresponding to thereference mark is extracted from the picked-up images so as to calculatethe amount of displacement of the reference mark in the directionperpendicular to the displacement detecting direction. Thus, the amountof displacement can be calculated at speed by non-contact imageprocessing, and control operations which provide excellent followingability can be performed.

(l) Twelfth Modification

A preferred embodiment of the twelfth modification is a method of thetenth modification, in which the vertical direction displacementdetecting step comprises: an image pick-up step of picking up images ofthe measuring plate; and a displacement calculating step of calculatingthe amount of displacement of the reference mark in the directionperpendicular to the displacement detecting direction by extracting theimage corresponding to the reference mark from the picked-up images.

According to the modification, images of the measuring plate are pickedup in the image pick-up step, and the image corresponding to thereference mark is extracted from the picked-up images so as to calculatethe amount of displacement of the reference mark in the directionperpendicular to the displacement detecting direction. Thus, the amountof displacement can be calculated at speed by non-contact imageprocessing, and control operations which provide excellent followingability can be performed.

E: Fifth Embodiment

The following is a description of the fifth preferred embodiment of thepresent invention, with reference to the accompanying drawings.

The object of the fifth embodiment is to provide a displacementdetecting device and a wheel alignment measuring device as well as adisplacement detecting method and a wheel alignment measuring method, bywhich accurate displacement measurements can be taken regardless of theshape of the measuring figure, and accurate non-contact wheel alignmentmeasurements can be taken at high speed.

The structure of the wheel alignment measuring device of the fifthembodiment is the same as in the fourth embodiment.

Measuring Operations

Here, the first circular mark MC1 should be always included in an imagepicked up by the color CCD camera 5A that constitutes the image pick-upunit 5, and the measuring plate 4B is attached to the wheel 3 of themeasured vehicle 2 so that the origin O of the measuring surface 4Scorresponds to the rotational center axis of the wheel 3.

FIG. 55 is a flowchart of the measuring operations. Like referencenumerals are allotted to like components in FIG. 55 and FIG. 14 of thefirst embodiment.

As in the first embodiment, the wheel 3 of the measured vehicle 2 isfirst driven upward or downward by an actuator (not shown),independently of other wheels. The actuator is then stopped at the emptyvehicle weight to maintain a stopped state (step S1).

The holding plate 10 and the image pick-up unit 5 are driven in theZ-axis direction by hand or by actuating the Z-axis direction drivingunit 12 and the X-axis direction driving unit 14 so that they face tothe measuring surface 4S of the measuring plate 4, the optical axes ofthe color CCD cameras 5A and 5B that constitute the image pick-up unit 5are arranged in line with the origin O of the measuring surface 4S, andthe measuring laser irradiation points P1 to P3 (see FIG. 53A) of thelaser displacement gauges 6-1 to 6-3 are set within the distancemeasuring area MLA (step S2C).

As in the first embodiment, the following operations are carried out:picking up images of the measuring surface 4S of the measuring plate 4by the image pick-up unit 5 (step S3); outputting the first picked-upimage data DGG1 and the second picked-up image data DGG2 (step S4);performing color separation by the color separation circuit 27 (stepS5); detecting the first circular mark MC1 by conducting a rough searchat DN-dot intervals (step S6); detecting the first circular mark MC1 byconducting a fine search with a scan in the positive direction of theX-axis at 1-dot intervals (step S7); calculating the Z-axis centercoordinate Z0 (step S8); detecting the first circular mark MC1 byconducting a rough search at CN-dot intervals with a scan in thepositive direction of the Z-axis (step S9); and detecting the firstcircular mark MC1 by conducting a fine search in the positive directionof the X-axis at 1-dot intervals (equivalent to intervals of L5A/NN mm)until the first circular mark MC1 can no longer be detected, storing thedot number M1 (=1 to NN) in the X-axis direction when the first circularmark MC1 is detected for the last time, and conducting a fine search ofthe first circular mark MC1 in the negative direction of the X-axis(step S10).

In step S10, when the first circular mark MC1 becomes undetectableagain, the X-axis center coordinate X0 is calculated based on the dotnumber M2 (=1 to NN) in the X-axis direction at the last detection ofthe first circular mark MC1 (step S11B).

As shown in FIG. 24 of the first embodiment, the correction lines CL aresubjected to sampling based on a white image obtained by adding thesecond red picked-up image data DR2, the second green picked-up imagedata DG2, and the second blue picked-up image data DB2 outputted fromthe color CCD camera 5B, and the inclination θ of the correction linesCL is calculated from the positional data by the method of least squares(step S12B).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the center coordinates (X0, Z0) of the first circular mark MC1determined in steps S8 and S11B and the center coordinates CCB of thevisual field ARB of the color CCD camera 5B is calculated (step S13B).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the position of the visualfield ARB can be roughly detected.

While calculating the center coordinates (X0, Z0) of the first circularmark MC1 and the distance LL, the arithmetic operation unit 28 alsocalculates the distance from the first circular mark MC1 on themeasuring surface 4S of the measuring plate 4, based on the outputsignals DLD1 to DLD3 of the laser displacement gauges 6-1 to 6-3.

The distance LL is then converted into the amount of displacement(travel distance) of the first circular mark MC1 on the measuringsurface 4S. To cancel the amount of displacement, the Z-axis directionstepping motor 11 of the Z-axis direction driving unit 12 and the X-axisdirection stepping motor 13 of the X-axis direction driving unit 14 aredriven so as to drive the holding plate 10 in the X-axis direction andthe Z-axis direction following the track of the first circular mark MC1.Even if the measuring surface 4S is inclined during measurement as shownin FIG. 53C, the measuring laser irradiation points P1 to P3 of thelaser displacement gauges 6-1 to 6-3 are situated within the distancemeasuring area MLA, regardless of the position of the optical axis ofthe color CCD camera 5B.

As a result, the measuring laser irradiation points P1 to P3 of thelaser displacement gauges 6-1 to 6-3 are always situated within thedistance measuring area MLA, so that a position Y as displacementinformation in the Y direction can be surely obtained, and that highlyreliable wheel alignment measurements can be taken in the Y direction aswell.

As in the first embodiment, the following steps are then carried out:calculating the distance da between the center coordinates CCA of thevisual field ARA and the center coordinates (X0, Z0) of the firstcircular mark MC1 (step S16); calculating the angle θa formed by avirtual line in parallel with the correction line CL extending throughthe center coordinates of the visual field ARA with respect to the lineconnecting the center coordinates of the visual field ARA and the centercoordinates of the first circular mark MC1 (step S17); calculating thedistance Xa and the distance Ya (step S18); calculating the position ofthe second circular mark MC2 n closest to the center coordinates of thevisual field ARA by counting the number (nx) of second circular markssituated between the closest second circular mark MC2 n and the firstcircular mark MC1 in the X direction, and the number (ny) of the secondcircular marks in the Z direction (step S19); calculating the distancesXb and Yb between the center coordinates (X0, Z0) of the second circularmark MC2 n closest to the center coordinates of the visual field ARA andthe center coordinates of the first circular mark MC1 (step S20); andcalculating the angle θi (low accuracy) formed by the X-axis of thevisual field ARA and the distance dd (low accuracy) between the centercoordinates of the visual field ARA and the center coordinates of thesecond circular mark MC2 n closest to the center coordinates of thevisual field ARA (step S21).

Further steps are carried out as in the first embodiment: calculatingthe low accuracy distances Xi and Yi between the center coordinates ofthe visual field ARA and the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARA(step S22); converting the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARB ofthe color CCD camera 5B into a dot address (IX, IY) (step S23);calculating the angle θb (high accuracy) formed by the X-axis of thevisual field ARA and the distance Db (high accuracy) between the centercoordinates of the visual field ARB and the center coordinates of theclosest second circular mark MC2 n in the visual field ARB of the colorCCD camera 5B (step S24); calculating the high accuracy distances Xc andYc between the center coordinates of the visual field ARB and the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB (step S25); converting the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB of the color CCD camera 5B into adot address (X, Y) (step S26); and transforming the dot address (X, Y)into the system of coordinates including the X-axis and Z-axis on themeasuring surface 4S of the measuring plate 4, so as to calculate a dotaddress (x, y) in the system of coordinates including the X-axis andZ-axis on the measuring surface 4S (step S27).

The arithmetic operation unit 28 next calculates the caster angle basedon the inclination of the scale line with respect to the horizontaldirection (or the vertical direction) of the picked-up image (stepS28D).

Based on the center coordinates (X0, Z0) of the first circular mark MC1,the Z-axis direction stepping motor 11 of the Z-axis direction drivingunit 12 and the X-axis direction stepping motor 13 of the X-axisdirection driving unit 14 are subjected to servo control, so that theholding plate 10 follows the track of the center of the first circularmark MC1.

Based on the secure output signals DLD1 to DLD3 obtained when themeasuring laser irradiation points P1 to P3 of the laser displacementgauges 6-1 to 6-3 are always within the distance measuring area MLA, thecamber angle is calculated from the differences in geometric distancefrom the measuring laser irradiation points P1 to P3 on the measuringsurface 4S of the measuring plate 4 corresponding to the laserdisplacement gauges 6-1 to 6-3, respectively (step S29D).

The arithmetic operation unit 28C then outputs the obtained dot addressx as X-coordinate data DX, the obtained dot address y as Z-coordinatedata DZ, the obtained spin angle as inclination data DSP, and theobtained camber angle as camber angle data DCB.

As described so far, according to the fifth embodiment, the laserdisplacement gauges 6-1 to 6-3 follow the displacement of the centercoordinates of the first circular mark MC1, which is the reference mark,so that the displacement in the Y direction (more specifically, theposition Y and the camber angle) can be calculated speedily andaccurately, based on the output signals DLD1 to DLD3 of the laserdisplacement gauges 6-1 to 6-3 in a driven state in such a direction asto cancel the displacement.

Based on picked-up images of the two color CCD cameras 5A and 5B, theposition and the spin angle corresponding to the center coordinates ofthe first circular mark MC1 on the measuring surface 4S of the measuringplate situated in a predetermined position (in the center in the aboveexample) within the image picked up by the color CCD camera 5B can becalculated speedily and accurately. Thus, reproducibility of themeasurement is improved.

As described above so far, according to this embodiment the wheelalignment can be measured speedily and accurately, and itsreproducibility and reliability can be improved.

Modifications of the Fifth Embodiment

(a) First Modification

A preferred embodiment of the first modification is a displacementdetecting device which detects the displacement of the measuring platein the displacement detecting direction, which is a directionperpendicular to the measuring surface of the measuring plate arrangedin a predetermined reference position. The displacement detecting devicecomprises: a vertical direction displacement detecting unit whichdetects the amount of displacement of the reference mark on themeasuring surface in a direction perpendicular to the displacementdetecting direction, and then outputs vertical direction displacementdetection data; a plurality of distance measuring units which measurethe distance from the measuring area by irradiating measuring light ontothe optically uniform measuring area on the measuring plate, and thenoutput distance measurement data; a driving unit which drives thedistance measuring units in such a direction as to cancel the amount ofdisplacement of the reference mark in the direction perpendicular to thedisplacement detecting direction, based on the vertical directiondisplacement detection data; and a detecting unit which detectsdisplacement of the measuring plate based on the distance measurementdata, and then outputs displacement detection data.

In this modification, the vertical direction displacement detecting unitdetects the amount of displacement of the reference mark on themeasuring surface in the direction perpendicular to the displacementdetecting direction, and then outputs the vertical directiondisplacement detection data to the driving unit; the driving unit drivesthe distance measuring units in such a direction as to cancel the amountof displacement of the reference mark in the direction perpendicular tothe displacement detecting direction; the distance measuring unitsmeasure the distance from the measuring area by irradiating themeasuring light onto the optically uniform measuring area on themeasuring plate, and then output the distance measurement data to thedetecting unit; and the detecting unit detects displacement of themeasuring plate based on the distance measurement data, and then outputsthe displacement detection data. Thus, the measuring light alwaysirradiate the optically uniform measuring area, and accuratedisplacement detection data can be outputted.

Since the non-contact and accurate displacement detection data can bequickly obtained, accurate wheel alignment measurements can be taken atspeed.

(b) Second Modification

A preferred embodiment of the second modification is a displacementmeasuring device of the first modification, in which the reference markis situated on an axis extending through the center of the wheel and inparallel with the displacement detecting direction.

Since the reference mark is situated on the axis extending through thecenter of the wheel and in parallel with the displacement detectingdirection, the driving unit drives the distance measuring units in sucha direction as to cancel the amount of displacement of the center of thewheel in a direction perpendicular to the displacement detectingdirection, so that the amount of displacement can be calculated in linewith the center of the wheel. Thus, the amount of displacement can becalculated under certain conditions, and wheel alignment measurementscan be steadily taken.

(c) Third Modification

A preferred embodiment of the third modification is a displacementmeasuring device of the first modification, in which the verticaldirection displacement detecting unit comprises: an image pick-up unitwhich picks up images of the measuring plate and outputs picked-up imagedata; and a displacement calculating unit which calculates the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction by extracting image data correspondingto the reference mark from the picked-up image data, and outputs thevertical direction displacement detection data.

In this modification, the image pick-up unit of the vertical directiondisplacement detecting unit picks up images of the measuring plate tooutput the picked-up image data to the displacement calculating unit;the displacement calculating unit extracts the image data correspondingto the reference mark from the picked-up image data to calculate theamount of displacement of the reference mark in the directionperpendicular to the displacement detecting direction, and outputs thevertical direction displacement detection data to the driving unit.Thus, displacement of the reference mark, i.e., displacement of themeasuring plate, can be speedily and accurately detected, and theirradiation points of the measuring light can be maintained in fixedpositions so as to carry out accurate displacement detection.

(d) Fourth Modification

A preferred embodiment of the fourth modification is a displacementdetecting device of the first modification, in which the driving unitcomprises: a first driving unit for driving the distance measuring unitin a first direction; a second driving unit for driving the distancemeasuring unit in a second direction perpendicular to the firstdirection; and a driving control unit for controlling the first drivingunit and the second driving unit based on the vertical directiondisplacement detection data.

In this modification, the driving control unit of the driving unitcontrols the first driving unit and the second driving unit based on thevertical direction displacement detection data; the first driving unitdrives the distance measuring unit in the first direction; and thesecond driving unit drives the distance measuring unit in the seconddirection perpendicular to the first direction. Because of thisstructure, the displacement of the reference mark can be accuratelyfollowed, and the irradiation points of the measuring light remain inthe same positions. Thus, accurate displacement detection can be carriedout.

(e) Fifth Modification

A preferred embodiment of the fifth modification comprises: a measuringplate which is attached to a wheel of the vehicle and has an opticallyuniform measuring area; a vertical direction displacement detecting unitwhich detects the amount of displacement of the reference mark in adirection perpendicular to the displacement detecting direction on themeasuring surface of the measuring plate, and outputs vertical directiondisplacement detection data; a plurality of distance measuring unitswhich measure the distance from the measuring area by irradiatingdistance measuring light upon the measuring area, and then outputdistance measurement data; a driving unit which drives the distancemeasuring units in such a direction as to cancel the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction, based on the vertical directiondisplacement detection data; a detecting unit which detects displacementof the measuring plate based on the distance measurement data, andoutputs displacement detection data; and a calculating unit whichcalculates wheel alignment measurement data based on the displacementdetection data.

In this modification, the vertical direction displacement detecting unitdetects the amount of displacement in a direction perpendicular to thedisplacement detecting direction of the reference mark on the measuringsurface of the measuring plate which is attached to a wheel of thevehicle and has an optically uniform measuring area, and then outputsthe vertical direction displacement detection data to the driving unit;the driving unit drives the distance measuring units in such a directionas to cancel the amount of displacement of the reference mark in adirection perpendicular to the displacement detecting direction, basedon the vertical direction displacement detection data; the plurality ofdistance measuring units measure the distance from the measuring area byirradiating the distance measuring light upon the measuring area, andeach of them outputs the distance measurement data to the detectingunit; the detecting unit detects displacement of the measuring platebased on the distance measurement data, and then outputs thedisplacement detection data to the calculating unit; and the calculatingunit calculate the wheel alignment measurement data based on thedisplacement detection data. With the distance measuring lightirradiating the optically uniform measuring area, accurate displacementdetection data are obtained. Based on the displacement detection data,non-contact wheel alignment measurements can be taken speedily andaccurately.

(f) Sixth Modification

A preferred embodiment of the sixth modification is a wheel alignmentmeasuring device of the fifth modification, in which the verticaldirection displacement detecting unit comprises: an image pick-up unitwhich picks up images of the measuring plate and outputs picked-up imagedata; and a displacement calculating unit which extracts image datacorresponding to the reference mark from the picked-up image data,calculates the amount of displacement of the reference mark in adirection perpendicular to the displacement detecting direction, andoutputs the vertical direction displacement detection data.

In this modification, the image pick-up unit picks up images of themeasuring plate and outputs the picked-up image data to the displacementcalculating unit; and the displacement calculating unit extracts imagedata corresponding to the reference mark from the picked-up image data,calculates the amount of displacement of the reference mark in adirection perpendicular to the displacement detecting direction, andthen outputs the vertical direction displacement detection data to thedriving unit. With the distance measuring light always irradiating theoptically uniform measuring area, accurate displacement detecting datacan be obtained.

Thus, with the non-contact accurate displacement detection data,accurate wheel alignment measurements can be taken speedily andaccurately.

(g) Seventh Modification

A preferred embodiment of the seventh modification is a displacementdetecting method of detecting displacement of the measuring plate in thedisplacement detecting direction, which is perpendicular to themeasuring surface of the measuring plate placed in a predeterminedreference position. The displacement detecting method comprises: avertical direction displacement detecting step of detecting the amountof displacement of the reference mark on the measuring surface in adirection perpendicular to the displacement detecting direction; adistance measuring step of measuring the distance from each irradiationpoint by irradiating distance measuring light upon several points on theoptically uniform measuring area on the measuring plate; a distancemeasuring position control step of controlling the irradiating points ofthe distance measuring light to be within the measuring area on themeasuring plate, based on the amount of displacement of the referencemark in a direction perpendicular to the displacement detectingdirection; and a detecting step of detecting displacement of themeasuring plate based on the distances from the irradiating points.

According to this modification, the amount of displacement of thereference mark on the measuring surface of the measuring plate in adirection perpendicular to the displacement detecting direction isdetected in the vertical direction displacement detecting step; thedistance measuring light irradiates several points on the opticallyuniform measuring area on the measuring plate, so that the distance fromeach irradiation point can be measured in the distance measuring step;based on the amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, the irradiationpoints on the measuring plate are controlled to be in predeterminedpositions within the measuring area in the distance measuring positioncontrol step; and based on the distances from the irradiation points,displacement of the measuring plate is detected in the detecting step.With the distance measuring light always irradiating the opticallyuniform measuring area, accurate displacement detection data can beobtained.

As the non-contact accurate displacement detection data can be obtained,accurate wheel alignment measurements can be taken at speed.

(h) Eighth Modification

A preferred embodiment of the eighth modification is a displacementmeasuring method of the seventh modification, in which the referencemark is situated on the axis in parallel with the displacement detectingdirection extending through the center of the wheel.

In this modification, with the reference mark situated on the axis inparallel with the displacement measuring direction extending through thecenter of the wheel, the driving unit drives the distance measuringunits in such a direction as to cancel the amount of displacement of thecenter of the wheel in a direction perpendicular to the displacementdetecting direction. Because of this, the amount of displacement can becalculated in line with the movement of the center of the wheel. Thus,the amount of displacement can be detected under certain conditions, andwheel alignment measurements can be steadily taken.

(i) Ninth Modification

A preferred embodiment of the ninth modification is a displacementdetecting method of the seventh modification, in which the verticaldirection displacement detecting step comprises: an image pick-up stepof picking up images of the measuring plate; and a displacementcalculating step of calculating the amount of displacement of thereference mark in a direction perpendicular to the displacementdetecting direction by extracting a picked-up image corresponding to thereference mark from the picked-up images of the measuring plate.

According to this modification, images of the measuring plate are pickedup in the image pick-up step of the vertical direction displacementdetecting step; and the amount of displacement of the reference mark ina direction perpendicular to the displacement detecting direction iscalculated by extracting the picked-up image corresponding to thereference mark from the picked-up images of the measuring plate in thedisplacement calculating step. Thus, displacement of the reference mark,i.e., displacement of the measuring plate, can be detected speedily andaccurately, and with the irradiation points of the distance measuringlight kept in certain positions, accurate displacement detection can becarried out.

(j) Tenth Modification

A preferred embodiment of the tenth modification is a displacementdetecting method of the seventh modification, in which the driving stepcomprises: a first driving step of driving the irradiation points of thedistance measuring light in a first direction; a second driving step ofdriving the irradiation points of the distance measuring light in asecond direction perpendicular to the first direction; and a drivingcontrol step of controlling the amount of driving in the first directionand the amount of driving in the second direction based on the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction.

According to this modification, the amount of driving in the firstdirection and the amount of driving in the second direction arecontrolled based on the amount of displacement of the reference mark ina direction perpendicular to the displacement detecting direction in thedriving control step; the irradiation points of the distance measuringlight is driven in the first direction in the first driving step; andthe irradiation points of the distance measuring light is driven in thesecond direction in the second driving step. With the irradiation pointsof the distance measuring light maintained in predetermined positions inline with displacement of the reference mark, accurate displacementdetection can be carried out.

(k) Eleventh Modification

A preferred embodiment of the eleventh modification comprises: avertical direction displacement detecting step of detecting the amountof displacement of the reference mark on the measuring surface of themeasuring plate in a direction perpendicular to the displacementdetecting direction; a distance measuring step of measuring thedistances from the irradiation points by irradiating the distancemeasuring light upon several points in the optically uniform measuringarea on the measuring surface; a driving step of driving the irradiationpoints of the distance measuring light in such a direction as to cancelthe amount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction, based on theamount of displacement of the reference mark in a directionperpendicular to the displacement detecting direction; a detecting stepof detecting displacement of the measuring plate based on the distancesfrom the irradiation points of the distance measuring light; and acalculating step of calculating the wheel alignment based on thedetected displacement of the measuring plate.

According to this modification, in the vertical direction displacementdetecting step, the amount of displacement of the reference mark on themeasuring surface of the measuring plate in a direction perpendicular tothe displacement detecting direction is detected.

In the distance measuring step, the distances from the irradiationpoints are measured by irradiating the distance measuring light uponseveral points in the optically uniform measuring area on the measuringsurface.

In the driving step, based on the amount of displacement of thereference mark in a direction perpendicular to the displacementdetecting direction, the irradiation points of the distance measuringlight are driven in such a direction as to cancel the amount ofdisplacement of the reference mark in a direction perpendicular to thedisplacement detecting direction.

In the detecting step, displacement of the measuring plate is detectedin accordance with the result of the driving step and the distances fromthe irradiation points of the distance measuring light. In thecalculating step, the wheel alignment is calculated based on thedetected displacement of the measuring plate. With the distancemeasuring light always irradiating the optically uniform measuring area,accurate displacement detection can be carried out. By measuring thewheel alignment based on the detected displacement, wheel alignmentmeasurements can be taken speedily and accurately in a non-contactmanner.

(l) Twelfth Modification

A preferred embodiment of the twelfth modification is a method of theeleventh modification, in which the vertical direction displacementdetecting step comprises: an image pick-up step of picking up images ofthe measuring plate to obtain picked-up images; and a displacementcalculating step of calculating the amount of displacement of thereference mark in a direction perpendicular to the displacementdetecting direction by extracting the image corresponding to thereference mark from the picked-up images.

According to this modification, images of the measuring plate are pickedup to obtain picked-up images in the image pick-up step; and the amountof displacement of the reference mark in a direction perpendicular tothe displacement detecting direction is calculated by extracting theimage corresponding to the reference mark in the displacementcalculating step. With the distance measuring light always irradiatingthe optically uniform measuring area, accurate displacement detectiondata can be obtained.

With the non-contact accurate displacement detection data, wheelalignment measurements can be taken speedily and accurately.

F: Sixth Embodiment

The following is a description of the sixth embodiment of the presentinvention, with reference to the accompanying drawings.

In this embodiment, the structure of the wheel alignment measuringdevice and the structure of the measuring unit are the same as in thefourth embodiment.

Structure of the Data Processing Control Unit

FIG. 56 is a block diagram illustrating the structure of the dataprocessing control unit 8E. Like reference numerals are allotted to likecomponents in FIG. 56 and FIG. 52 of the fourth embodiment.

The data processing control unit 8E comprises a display 25, an X-Z pulsemotor control unit 26, a color separation circuit 27, and an arithmeticoperation unit 28E. The display 25 displays an image based on either thefirst picked-up image data DGG1 outputted from the color CCD camera 5Aor the second picked-up image data DGG2 outputted from the color CCDcamera 5B. The X-Z pulse motor control unit 26 controls the driving ofthe Z-axis stepping motor 11 and the X-axis stepping motor 14, based onposition control data DPC. The color separation circuit 27 performscolor separation based on the first picked-up image data DGG1 and thesecond picked-up image data DGG2 outputted from the image pick-up unit5, and outputs red picked-up image data DR corresponding to red, greenpicked-up image data DG corresponding to green, and blue picked-up imagedata DB corresponding to blue. Based on output signals DLD1 to DLD3 fromthe three laser displacement gauges 6-1 to 6-3, the red picked-up imagedata DR, the green picked-up image data DG, and the blue picked-up imagedata DB, the arithmetic operation unit 28E outputs: X-coordinate data Xon the measuring surface 4S of the measuring plate 4 in a predeterminedposition in a high-resolution picked-up image (for instance, the centerof the picked-up image); Y-coordinate data Y of the measuring surface4S; Z-coordinate data Z on the measuring surface 4S of the measuringplate 4 in a predetermined position in a high-solution picked-up image;an inclination θx with respect to the X-axis on the measuring surface4S; an inclination θy with respect to the Y-axis on the measuringsurface 4S; an inclination θz with respect to the Z-axis on themeasuring surface 4S; the effective caster angle θECAS and camber angledata θCAM obtained based on the inclinations θx, θy, and θz; and theposition control data DPC.

Here, the red picked-up image data DR include first red picked-up imagedata DR1 corresponding to the first picked-up image data DGG1 and secondred picked-up image data DR2 corresponding to the second picked-up imagedata DGG2, the green picked-up image data DG include first greenpicked-up image data DG1 corresponding to the first picked-up image dataDGG1 and second green picked-up image data DG2 corresponding to thesecond picked-up image data DGG2, and the blue picked-up image data DBinclude first blue picked-up image data DB1 corresponding to the firstpicked-up image data DGG1 and second blue picked-up image data DB2corresponding to the second picked-up image data DGG2.

Caster Angle Measuring Operation

Prior to describing the wheel alignment measuring operation, the casterangle measuring operation will be described below.

In order to carry out a caster angle measuring operation, the casterangle detecting line CL is extracted by obtaining a logical product(AND) of the first red picked-up image data DR1, the first greenpicked-up image data DG1, and the first blue picked-up image data DB1,or by obtaining a logical product (AND) of the second red picked-upimage data DR2, the second green picked-up image data DG2, and thesecond blue picked-up image data DB2, based on the first red picked-upimage data DR1 corresponding to the first picked-up image data DGG1, thesecond red picked-up image data DR2 corresponding to the secondpicked-up image data DGG2, the first green picked-up image data DG1corresponding to the first picked-up image data DGG1, the second greenpicked-up image data DG2 corresponding to the second picked-up imagedata DGG2, the first blue picked-up image data DB1 corresponding to thefirst picked-up image data DGG1, and the second blue picked-up imagedata DB2 corresponding to the second picked-up image data DGG2, alloutputted by the color separation circuit 27 performing color separationon the image data DGG1 and DGG2 of the color CCD cameras 5A and 5B.

By the method of least squares, the inclination (=b/a) of the casterangle detecting line CL with respect to a virtual reference line LREF(shown by a broken line in FIG. 57) arranged in advance is calculated.

If standard color CCD cameras having 400×400 dots are employed as thecolor CCD cameras 5A and 5B here, the minimum caster angle data θCASmin,which are detectable using the caster angle detecting line CL extractedbased on the image data DGG1 and DGG2 and the virtual reference lineLREF determined in advance, correspond to the case where the gradient ofthe caster angle detecting line CL changes by 1 dot in every 400 dots,as shown in FIG. 58. This is expressed as:

θCASmin=tan⁻¹(1 dot/400 dots)=0.14°

Here, a caster angle having a smaller angle than the minimum casterangle data θCASmin is undetectable and becomes a dead zone.

Meanwhile, in alignment measurement for a vehicle, the caster angle dataneed to have a measuring accuracy of ±0.01°.

In view of this, the caster angle data based on the image data DGG1 andDGG2 obtained by the color CCD cameras 5A and 5B are too low inmeasuring accuracy to be used as data in an alignment measuringoperation.

More specifically, the real caster angle varies constantly as shown inFIG. 59A. However, when measured by the color CCD cameras 5A and 5B, thecaster angle data vary at certain intervals as shown in FIGS. 59B and60, changing from 0° to 0.14° to 0.28°, with the maximun error being0.14° or less. In actual wheel alignment measurement, the caster anglemonotonously increases or decreases as shown in FIG. 61. In view of themachine accuracy of the color CCD cameras 5A and 5B, the accuracy of thecaster angle data, which are obtained when the value of the caster angledata θCAS changes, can be maintained in the range of ±0.01°.

The high accuracy caster angle data θCAS serve as the effective casterangle data θECAS, and are compared with the data N4, N9, and N15 (seeFIGS. 59 and 60) of the corresponding timing among the data N1 to N15 ofother dimensions such as camber angle and toe angle.

As a result, the data pitch becomes 0.14°, but the desired accuracy canbe maintained during data processing.

As caster angle measurements can be taken in a non-contact mannerthrough image processing, high durability and speed can be maintained.

Next, the description moves on to the wheel alignment measuringoperation.

Measuring Operations

Here, the first circular mark MC1 should be always included in an imagepicked up by the color CCD camera 5A that constitutes the image pick-upunit 5, and the measuring plate 4 is attached to the wheel 3 of themeasured vehicle 2 so that the origin O of the measuring surface 4Scorresponds to the rotational center axis of the wheel 3.

FIG. 62 is a flowchart of the measuring operations. Like referencenumerals are allotted to like components in FIG. 62 and FIG. 14 of thefirst embodiment.

As in the first embodiment, the wheel 3 of the measured vehicle 2 isfirst driven upward or downward by an actuator (not shown) independentlyof other wheels. The actuator is then stopped at the empty vehicleweight to maintain a stopped state (step S1).

The holding plate 10 and the image pick-up unit 5 are driven in theZ-axis direction by hand or by actuating the Z-axis direction drivingunit 12 and the X-axis direction driving unit 14 so that they face tothe measuring surface 4S of the measuring plate 4, the optical axes ofthe color CCD cameras 5A and 5B that constitute the image pick-up unit 5are arranged in line with the origin O of the measuring surface 4S, andthe measuring laser irradiation points P1 to P3 (see FIG. 53A) of thelaser displacement gauges 6-1 to 6-3 are set within the distancemeasuring area MLA (step S2C).

As in the first embodiment, the following operations are carried out:picking up images of the measuring surface 4S of the measuring plate 4by the image pick-up unit 5 (step S3); outputting the first picked-upimage data DGG1 and the second picked-up image data DGG2 (step S4);performing color separation by the color separation circuit 27 (stepS5); detecting the first circular mark MC1 by conducting a rough searchat DN-dot intervals (step S6); detecting the first circular mark MC1 byconducting a fine search with a scan in the positive direction of theX-axis at 1-dot intervals (step S7); calculating the Z-axis centercoordinate Z0 (step S8); detecting the first circular mark MC1 byconducting a rough search at CN-dot intervals with a scan in thepositive direction of the Z-axis (step S9); and detecting the firstcircular mark MC1 by conducting a fine search in the positive directionof the X-axis at 1-dot intervals (equivalent to intervals of L5A/NN mm)until the first circular mark MC1 can no longer be detected, storing thedot number M1 (=1 to NN) in the X-axis direction when the first circularmark MC1 is detected for the last time, and conducting a fine search ofthe first circular mark MC1 in the negative direction of the X-axis(step S10).

In step S10, when the first circular mark MC1 becomes undetectableagain, the X-axis center coordinate X0 is calculated based on the dotnumber M2 (=1 to NN) in the X-axis direction at the last detection ofthe first circular mark MC1 (step S11B).

As shown in FIG. 24 of the first embodiment, the correction lines CL aresubjected to sampling based on a white image obtained by adding thesecond red picked-up image data DR2, the second green picked-up imagedata DG2, and the second blue picked-up image data DB2 outputted fromthe color CCD camera 5B, and the inclination e of the correction linesCL is calculated from the positional data by the method of least squares(step S12B).

Based on the image picked up by the color CCD camera 5A, the distance LLbetween the center coordinates (X0, Z0) of the first circular mark MC1determined in steps S8 and S11B and the center coordinates CCB of thevisual field ARB of the color CCD camera 5B is calculated (step S13B).

By doing so, the correction lines CL surrounding the center coordinatesof the visual field ARB can be specified, and the position of the visualfield ARB can be roughly detected.

As in the first embodiment, the following steps are then carried out:calculating the distance da between the center coordinates CCA of thevisual field ARA and the center coordinates (X0, Z0) of the firstcircular mark MC1 (step S16); calculating the angle θa formed by avirtual line in parallel with the correction line CL extending throughthe center coordinates of the visual field ARA with respect to the lineconnecting the center coordinates of the visual field ARA and the centercoordinates of the first circular mark MC1 (step S17); calculating thedistance Xa and the distance Ya (step S18); calculating the position ofthe second circular mark MC2 n closest to the center coordinates of thevisual field ARA by counting the number (nx) of second circular markssituated between the closest second circular mark MC2 n and the firstcircular mark MC1 in the X direction, and the number (ny) of the secondcircular marks in the Z direction (step S19); calculating the distancesXb and Yb between the center coordinates (X0, Z0) of the second circularmark MC2 n closest to the center coordinates of the visual field ARA andthe center coordinates of the first circular mark MC1 (step S20); andcalculating the angle θi (low accuracy) formed by the X-axis of thevisual field ARA and the distance dd (low accuracy) between the centercoordinates of the visual field ARA and the center coordinates of thesecond circular mark MC2 n closest to the center coordinates of thevisual field ARA (step S21).

Further steps are carried out as in the first embodiment: calculatingthe low accuracy distances Xi and Yi between the center coordinates ofthe visual field ARA and the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARA(step S22); converting the center coordinates of the second circularmark MC2 n closest to the center coordinates of the visual field ARB ofthe color CCD camera 5B into a dot address (IX, IY) (step S23);calculating the angle θb (high accuracy) formed by the X-axis of thevisual field ARA and the distance Db (high accuracy) between the centercoordinates of the visual field ARB and the center coordinates of theclosest second circular mark MC2 n in the visual field ARB of the colorCCD camera 5B (step S24); calculating the high accuracy distances Xc andYc between the center coordinates of the visual field ARB and the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB (step S25); converting the centercoordinates of the second circular mark MC2 n closest to the centercoordinates of the visual field ARB of the color CCD camera 5B into adot address (X, Y) (step S26); and transforming the dot address (X, Y)into the system of coordinates including the X-axis and Z-axis on themeasuring surface 4S of the measuring plate 4, so as to calculate a dotaddress (x, y) in the system of coordinates including the X-axis andZ-axis on the measuring surface 4S (step S27).

The arithmetic operation unit 28 next obtains the effective caster angledata θECAS by calculating the inclination of the caster line detectingline CL with respect to the horizontal direction (or the verticaldirection) of the picked-up image (step S28E).

Based on the output signals DLD1 to DLD3 of the laser displacementgauges 6-1 to 6-3, the camber angle is calculated from the differencesin geometric distance from the measuring surface 4S of the measuringplate 4 (step S29E).

The arithmetic operation unit 28C then outputs the obtained dot addressx as X-coordinate data DX, the obtained dot address y as Z-coordinatedata DZ, the obtained caster angle as the effective caster angle dataθECAS, and the obtained camber angle as camber angle data θcam.

According to this embodiment, the effective caster angle data θECAS canbe compared with data of other dimensions, such as the camber angle dataθCAM with desired accuracy.

Based on picked-up images of the two color CCD cameras 5A and 5B, thecaster angle can be calculated with desired precision and speed, andcompared with data of other dimensions (such as the camber angle data).Thus, reproducibility of the measurement is improved.

As described so far, according to this embodiment, the wheel alignmentcan be measured speedily and accurately, and its reproducibility andreliability can be improved.

G: Seventh Embodiment

The following is a description of the seventh embodiment of the presentinvention, with reference to the accompanying drawings.

Structure of the Alignment Measuring Device

FIG. 63 is a block diagram illustrating the wheel alignment measuringdevice. Like reference numerals are allotted to like components in FIG.63 and in the first embodiment.

The wheel alignment measuring device 1F comprises: a measuring plate 4Fattached to a wheel 3 of a measured vehicle 2; a measuring unit 7 whichpicks up images of the measuring surface 4S of the measuring plate 4F bya color CCD camera 5, and measures the distance from the measuringsurface 4S of the measuring plate by a plurality of laser displacementgauges 6; and a data processing unit 8F which performs an alignmentcalculating operation based on output signals from the measuring unit 7.

The data processing unit 8F comprises: a processor main body 8FA whichperforms various arithmetic operations based on the output signals fromthe measuring unit 7; a display 8FB which displays various kinds ofinformation under the control of the processor main body 8FA; a keyboard8FC for inputting various data into the processor main body 8FA; and aprinter 8FD which prints out the data under the control of the processormain body 8FA.

Structure of the Measuring Plate

FIG. 64 is a front view of the measuring plate.

On the measuring surface 4S of the measuring plate 4F, the base iscolored black, and three concentric circles having the same origin O arecolored green. The radius ratio of the concentric circles C1 to C3 areset as:

C1:C2:C3=1:2:3

However, the radius ratio of the concentric circles C1 to C3 is notlimited to the above example, as long as they can be distinguished fromone another based on curvature or the like through image processing.

Scale lines LX1 to LX7 in parallel with the X-axis are colored red andin contact with the corresponding concentric circles C1 to C3.

Scale lines LZ1 to LZ3 in parallel with the Z-axis are colored blue andin contact with the corresponding concentric circles C1 to C3.

In this embodiment, the scale lines LX1 to LX3 are perpendicular to thescale lines LZ1 to LZ3, and they are in contact with the concentriccircles C1 to C3. However, if the scale lines are drawn at predeterminedintervals and cross each other at a predetermined angle, the sameeffects can be achieved with more complicated arithmetic operations.

Structure of the Measuring Unit

FIG. 65 is an external perspective view of the measuring unit.

The measuring unit 7 comprises: a rhombic holding plate 10F having fourlaser displacement gauges 6-1 to 64; a CCD camera 5 which is provided onthe rear side of the holding plate 10F and picked-up images of themeasuring plate 4F through an opening 10FA formed in the center of theholding plate 10F; a Z-axis direction driving unit 12F which is providedwith a Z-axis direction driving knob 11F and drives the holding plate10F and the CCD camera 5 in the Z-axis direction when the Z-axisdirection driving knob 11F is rotated by the operator; an angledirection driving unit 14F which is provided with an angle directiondriving knob 13F and drives the holding plate 10F and the CCD camera 5in a direction indicated by an arrow A in FIG. 65 when the angledirection driving knob 13F is rotated by the operator; a Y-axisdirection driving unit 16F which is provided with a Y-axis directiondriving knob 15F and drives the holding plate 10F and the CCD camera 5in the Y-axis direction when the Y-axis direction driving knob 15F isrotated by the operator; an X-axis driving unit 18F which is providedwith an X-axis direction driving knob 17F and drives the holding plate10F and the CCD camera 5 in the X-axis direction when the X-axisdirection driving knob 17F is rotated by the operator; a base unit 19Fwhich holds the holding plate 10F, the CCD camera S, the Z-axisdirection driving unit 12F, the Y-axis direction driving unit 16F, andthe X-axis direction driving unit 18F; and a guide rail 20F for the baseunit 19F to slide in the X-axis direction.

Structure of the Processor Main Body

FIG. 66 is a block diagram illustrating the processor main body of thedata processing unit.

The processor main body 8FA comprises: a controller 15F for controllingthe entire processor main body 8FA; an interface 26F for interfacing thecontroller 25F, the display 8FB, the keyboard 8FC, and the printer 8FDwith one another; a color separation circuit 27F which performs colorseparation based on picked-up image data DCCD outputted from the CCDcamera 5, and then outputs red picked-up image data DR corresponding tored, green picked-up image data DG corresponding to green, and bluepicked-up image data DB corresponding to blue; and an arithmeticoperation unit 28F which calculates and outputs X-coordinate data DX andZ-coordinate data DZ on the measuring surface 4S of the measuring plate4F in a predetermined position of an image picked up by the CCD camera 5(at the center point of the picked-up image, for instance), andinclination (spin angle) data DSP on the inclination of the X-axis (orZ-axis) with respect to the reference direction, based on the outputsignals DLD1 to DLD4 of the four laser displacement gauges 6-1 to 6-4,the red picked-up image data DR, the green picked-up image data DG, andthe blue picked-up image data DB.

Measuring Operation

The following is a description of the measuring operation of thisembodiment, referring to FIGS. 67 to 69.

In this embodiment, at least one concentric circle or one scale lineshould be included in the image picked up by the CCD camera 5,regardless of which part of the measuring surface 4S of the measuringplate 4 is picked up. The measuring plate 4 is attached to the wheel 3of the measured vehicle 2 so that the origin O of the measuring surface4S corresponds to the rotational axis of the wheel 3.

FIG. 67 is a flowchart of the measuring operation.

First, the operator slides the base unit 19 on the guide rail 20 in theX-axis direction, or operates the Z-axis direction driving unit 12F (byoperating the Z-axis direction driving knob 11F), the angle directiondriving unit 14F (by operating the angle direction driving knob 13F),the Y-axis direction driving unit 16F (by operating the Y-axis directiondriving knob 15F), and the X-axis direction driving unit 18F (byoperating the X-axis direction driving knob 17F). Thus, the holdingplate 10F and the CCD camera 5 can face to the measuring surface 4S ofthe measuring plate 4F, and the center point CC of the image picked upby the CCD camera 5 (see FIG. 68) corresponds to the origin O of themeasuring surface 4S (step S3 1).

Next, the wheel 3 of the measured vehicle 2 is driven upward or downwardby an actuator (not shown) independently of other wheels. The actuatoris then stopped and kept in the stopped state (step S32).

The coordinates of the center point CC of the picked-up image FL arecalculated as follows:

A: In the Case Where One Concentric Circle and Two Scale Lines areContained in a Picked-up Image

FIG. 68 illustrates an image which is picked up by the CCD camera 5 andcontains one concentric circle and two scale lines.

The processor main body 8FA of the data processing unit 8 controls theCCD camera 5 of the measuring unit 7F to pick up an image of themeasuring surface 4S (step S33), and outputs picked-up image data DCCDto the color separation processing circuit 27 of the processor main body8A (step S34).

By doing so, the color separation circuit 27 performs color separationon the picked-up image data DCCD outputted from the CCD camera 5 underthe control of the controller 25, and then outputs red picked-up imagedata DR corresponding to red, green picked-up image data DGcorresponding to green, and blue picked-up image data corresponding toblue to the arithmetic operation unit 28F (step S35).

At the same time of the image pick-up process by the CCD camera 5, thefour laser displacement gauges 6-1 to 6-4 irradiate laser on themeasuring surface 4S of the measuring plate 4F, and outputs the outputsignals DLD1 to DLD4 corresponding to the distances from the measuringplate, to the arithmetic operation unit 28F (step S36).

The arithmetic operation unit 28F first extracts the concentric circleCXX (one of the concentric circles C1 to C3) in the picked-up image FLbased on the green picked-up image data DG, and performs distancecorrection in accordance with the output signals DLD1 to DLD4 tocalculate the curvature of the concentric circle CXX (step S37). Thearithmetic operation unit 28F then compares the obtained curvature withthe curvatures of concentric circles stored in advance, and judges whichconcentric circle is the concentric circle CXX (step S38).

In the following description, the radius of the distinguished concentriccircle CXX is R.

The arithmetic operation unit 28F judges the positions of the scalelines included in the picked-up image, based on the red picked-up imagedata DR and the blue picked-up image data DB (step S39).

With perpendicular lines drawn from the center point CC to the scalelines distinguished in step S39, the distance ΔX from the center pointCC to the scale line in parallel with the Z-axis and the distance ΔZfrom the center point C to the scale line in parallel with the X-axisare calculated (step S40).

If the perpendicular lines from the center point CC cross (or are incontact with) the concentric circle CXX, the scale lines circumscribethe concentric circle CXX. If the perpendicular lines do not cross theconcentric circle CXX, the scale lines circumscribe a concentric circlehaving the largest radius among concentric circles having a smallerradius than that of the concentric circle CXX, or pass through theorigin O.

In the case where the perpendicular lines cannot be drawn within thepicked-up image FL, they should be drawn toward lines extending from thescale lines on a virtual plane, so that the distances from the scalelines can be calculated.

The arithmetic operation unit 28F then determines the coordinates (XC,ZC) of the center point CC of the picked-up image FL, based on thedistances ΔX and ΔZ, and the coordinates of the scale lines (step S41).Whether the distances ΔX and ΔZ should be added or subtracted withrespect to the coordinates of the scale lines depends on the quadrant towhich the center point CC belongs. Therefore, it is necessary to judgecorrectly to which quadrant the center point CC belongs, based on theexpanding direction of the circumference of the concentric circle andthe extending direction of the scale lines.

More specifically, the situation shown in FIG. 68 can be expressed as:

(XC, ZC)=(R−ΔX, R−ΔZ)

The arithmetic operation unit 28F then determines the spin angle bycalculating the inclinations of the scale lines with respect to thehorizontal direction (or the vertical direction) of the picked-up image(step S42).

As a result, the arithmetic operation unit 28F outputs the centercoordinates XC as X-coordinate data DX, the center coordinates DZ asZ-coordinate data DZ, and the spin angle as inclination data DSP.

B: In the Case Where One Concentric Circle and One Scale Line areContained in a Picked-up Image

FIG. 69 shows an image which is picked up by the CCD camera 5 andcontains one concentric circle and one scale line.

The processor main body 8FA of the data processing unit 8F controls theCCD camera 5 of the measuring unit 7F to pick up an image of themeasuring surface 4S (step S33), and outputs pick-up data DCCD to thecolor separation circuit 27F of the processor main body 8FA (step S34).

By doing so, the color separating circuit 27F performs color separationon the picked-up image data DCCD outputted from the CCD camera 5 underthe control of the controller 25F, and outputs red picked-up image dataDR corresponding to red, green picked-up image data DG corresponding togreen, and blue picked-up image data DB corresponding to blue, to thearithmetic operation unit 28F (step S35).

At the same time of the image pick-up process by the CCD camera 5, thefour laser displacement gauges 6-1 to 6-4 irradiate laser onto themeasuring surface 4S of the measuring plate 4F, and outputs the outputsignals DLD1 to DLD4 corresponding to the distances from the measuringplate, to the arithmetic operation unit 28F (step S36).

The arithmetic operation unit 28F first extracts the concentric circleCXX (one of the concentric circles C1 to C3) in the picked-up image FLbased on the green picked-up image data DG, and performs distancecorrection in accordance with the output signals DLD1 to DLD4 tocalculate the curvature of the concentric circle CXX (step S37). Thearithmetic operation unit 28F then compares the obtained curvature withthe curvatures of concentric circles stored in advance, and judges whichconcentric circle is the concentric circle CXX (step S38).

In the following description, the radius of the distinguished concentriccircle CXX is R.

The arithmetic operation unit 28F judges the positions of the scale linecontained in the picked-up image, based on the red picked-up image dataDR and the blue picked-up image data DB (step S39).

With a perpendicular line drawn from the center point CC to the scaleline in parallel with the Z-axis distinguished in step S39, the distanceΔX1 from the center point CC to the scale line LZX in parallel with theZ-axis is calculated (step S40).

If the perpendicular line drawn from the center point CC crosses (or isin contact with) the concentric circle CXX, the scale line circumscribesthe concentric circle CXX. If the perpendicular line does not cross theconcentric circle CXX, the scale line circumscribes a concentric circlehaving the largest radius among concentric circles having a smallerradius than that of the concentric circle CXX, or pass through theorigin O.

In the case where the perpendicular line cannot be drawn within thepicked-up image FL, it should be drawn toward a line extending from thescale line on a virtual plane, so that the distance from the scale linecan be calculated.

The arithmetic operation unit 28F then determines the coordinates (XC,ZC) of the center point CC of the picked-up image FL, based on thedistances ΔX1 and the coordinates of the scale line LZX (step S41).

More specifically, with the perpendicular line drawn from the centerpoint CC of the picked-up image FL to the scale line LZX, theintersection is P1, and the distance from the center point CC to theintersection P1 is ΔX1.

The arithmetic operation unit 28F then draws a perpendicular line towardthe concentric circle CXX and extends the perpendicular line to thescale line LZX. The intersection of the perpendicular line and the scaleline LZX is P2. If extended in the opposite direction from the scaleline LZX, the perpendicular line passes through the origin O.

As a result, the triangle defined by CC, P1, and P2 becomes similar tothe triangle defined by O, PLZX, and P2. With the distance Z1 from theintersection P1 to the intersection P2 and the distance ZZ from theintersection P2 to the point PLZX, the relationships shown in FIG. 69can be expressed as:

R:ΔX 1=ZZ:Z 1

and

ZZ=(R·Z 1)/ΔX 1

Accordingly, the coordinates of the center point CC can be expressed as:

(XC, ZC)=(R−ΔX 1,ZZ−Z 1)

 =(R−ΔX 1,(R·Z 1)/ΔX 1−Z 1)

=(R−ΔX 1, {[R/ΔX 1]−1}·Z 1)

The arithmetic operation unit 28F then determines the spin angle bycalculating the inclinations of the scale lines with respect to thehorizontal direction (or the vertical direction) of the picked-up image(step S42).

As a result, the arithmetic operation unit 28F outputs the centercoordinates XC as X-coordinate data DX, the center coordinates DZ asZ-coordinate data DZ, and the spin angle as inclination data DSP.

As described so far, according to this embodiment, based on a picked-upimage containing at least one concentric circle and one scale line, theposition corresponding to the origin of the measuring surface 4S of themeasuring plate 4 in a predetermined position within the picked-up image(for instance, at the center point) can be calculated speedily andaccurately, which improves reproducibility of measurement.

Accordingly, wheel alignment measurements can be taken speedily andaccurately, and its reproducibility and reliability are improved in thisembodiment.

What is claimed is:
 1. A measuring plate attached to a wheel so that anorigin thereof corresponds to a rotational center of the wheel of avehicle being measured, comprising: a measuring mark area which isformed in an area surrounding and containing the origin, and providedwith measuring marks; and a distance measuring area on the measuringplate which distance measuring area is optically uniform and extendsalong an axis that is coaxial with a longitudinal direction of thevehicle being measured, said distance measuring area being irradiated bya measuring light emitted from a measuring unit, said measuring markarea containing: a first reference mark having center coordinates thatare the origin of said measuring plate; a plurality of second referencemarks having center coordinates that are located at intersections offirst virtual lines in parallel and second virtual lines in parallel;and a plurality of correction lines which are in parallel with eitherthe first virtual lines or the second virtual lines, and are situated atuniform intervals.
 2. A wheel alignment measuring device for measuringwheel alignment using said measuring plate of claim 1, comprising: atleast two distance measuring means each of which are configured foremitting and receiving the distance measuring light and for outputtingdistance measuring signals corresponding to the distance from saidmeasuring plate, said means being fixed in predetermined referencepositions at a predetermined distance from each other; and distancecalculating means for calculating the distance from a predeterminedposition on said measuring plate corresponding to the predeterminedreference positions, based on the distance measuring signals.
 3. A wheelalignment measuring device for measuring the distance from and theinclination of the measuring surface of a measured plate which isattached to a wheel of a vehicle being measured so that the originthereof corresponds to the center of the rotational axis of the wheel,comprising: said wheel alignment measuring device comprises at leastfour distance measuring light emitting and receiving means having lightemitting portions which are arranged on a same virtual plane atpredetermined intervals for emitting distance measuring light onto themeasuring surface, receiving the distance measuring light reflected bythe measuring surface, and outputting distance measuring signals, saidlight emitting portions being so arranged on the same virtual plane atintervals that the distance measuring light emitted from at least threeof the at least four distance measuring light emitting and receivingmeans impinges on the measuring surface under predetermined measuringconditions, the virtual plane is arranged so that it contains a straightline substantially in parallel with a vertical direction of the vehicleto be measured, a virtual parallelogram being arranged on the virtualplane so that the straight line includes one of the diagonal lines ofthe virtual parallelogram, the light emitting portions of the at leastfour distance measuring light emitting and receiving means are arrangedat each corner of the virtual parallelogram, and the virtualparallelogram is arranged so that the distance measuring light isemitted from the two light emitting portions on the other diagonal linenot included in the straight line within a common area for a firstmeasuring surface corresponding to a maximum distance moved by themeasuring surface in a first direction along the straight line, and asecond measuring surface corresponding to a maximum distance moved bythe measuring surface in a second direction opposite to the firstdirection.
 4. A wheel alignment measuring method for measuring, byemploying a measuring plate attached coaxially with a rotary axis of awheel, a distance from a measuring surface of the measuring plate, andan angle of inclination of the measuring surface, comprising the stepsof: emitting at least three out of at least four distance measuringlight beams spaced at predetermined intervals onto the measuring surfaceand receiving the distance measuring light beams reflected therefrom;and calculating a camber angle of the measuring surface based on thereceived distance measuring light beams, a virtual plane being arrangedso that it includes a straight line substantially in parallel with thevertical direction of the vehicle to be measured, the step of distancemeasuring light emitting and receiving being implemented by arranging avirtual parallelogram on the virtual plane so that the straight lineincludes one of the diagonal lines of the virtual parallelogram,emitting the distance measuring light beams from each apex of thevirtual parallelogram and receiving the distance measuring light beamsreflected at the measuring surface, the step of calculating camber anglebeing implemented by receiving reflected distance measuring light beamsemitted from two apexes on the other diagonal line not included in thestraight line onto a common area for a first measuring surfacecorresponding to a maximum distance moved by the measuring surface in afirst direction along the straight line, and a second measuring surfacecorresponding to a maximum distance moved by the measuring surface in asecond direction opposite to the first direction and by receivingreflected distance measuring light beam emitted from either one ofapexes on the diagonal line included in the straight line onto themeasuring surface.
 5. The wheel alignment measuring method according toclaim 4, wherein said camber angle calculating step includes the stepsof: choosing either one of said two distance measuring light beamsemitted from the apexes included in the straight line and reflected atthe measuring surface; and calculating the camber angle of the measuringsurface based on the distance measuring light beam chosen in saidchoosing step and two distance measuring light beams emitted from theother apexes not included in the straight line.
 6. A caster anglemeasuring device comprising: a wheel alignment measuring plate having ameasuring object thereon; a CCD camera for picking up an image of thewheel alignment measuring target plate; original caster angle datacalculating means for calculating original caster angle data θ CAS byquantizing a caster angle formed between a measuring object line and apredetermined reference line based on the image data; and output meansfor outputting the original caster angle data θ CAS as the effectivecaster angle data θ ECAS when the original caster angle data θ CASchanges its value.
 7. The caster angle measuring device according toclaim 6, wherein said original caster angle data calculating meanscomprises: line extracting means for extracting the measuring objectline based on the image data; and inclination calculating means forcalculating the inclination of the extracted measuring object line byapplying the method of least squares.
 8. A wheel alignment measuringdevice comprising: a CCD camera for outputting image data by picking upan image of a caster angle measuring object line provided on a wheelalignment measuring target plate attached to a vehicle; a caster anglemeasuring device for outputting effective caster angle data θECAS havinga desired measuring accuracy based on the image data obtained by pickingup an image, with use of the external CCD camera, of the caster anglemeasuring object line, comprising: original caster angle datacalculating means for calculating original caster angle data θ CAS byquantizing the caster angle formed between the measuring object line anda predetermined reference line based on the image data; and effectivedata output means for outputting the original caster angle data θ CAS asthe effective caster angle data θ ECAS when the original caster angledata θ CAS changes its value and data comparing means for comparing theeffective caster angle data θ ECAS with measured data of a differentdimension at substantially the same time when there is said change inthe original caster angle data θCAS.
 9. A caster angle measuring devicefor outputting effective caster angle data θ ECAS having a desiredmeasuring accuracy based on image data obtained by picking up an imagewith use of an external CCD camera, of a caster angle measuring objectline provided on a wheel alignment measuring target plate mounted on avehicle, comprising: original caster angle data calculating means forcalculating original caster angle data θ CAS based on the image datawhen the caster angle formed between the measuring object line and apredetermined reference line changes continuously in either direction ofincreasing or decreasing; comparing means for comparing original casterangle data θ CAS(n−1) measured in a previous measurement timing withoriginal caster angle data θ CAS(n) measured in a current measurementtiming; and effective data output means for outputting the originalcaster angle data θ CAS(n) of the current measurement as the effectivecaster angle data θ ECAS when the comparison results in: θ CAS(n−1)≠θCAS(n).
 10. The caster angle measuring device according to claim 9,wherein said original caster angle data calculating means comprises:line extracting means for extracting the measuring object line based onthe image data; and inclination calculating means for calculating theinclination of the extracted measuring object line by applying themethod of least squares.
 11. A wheel alignment measuring devicecomprising: a CCD camera for outputting image data by picking up animage of a caster angle measuring object line drawn on a wheel alignmentmeasuring target plate attached to a vehicle; a caster angle measuringdevice for outputting effective caster angle data θ ECAS having adesired measuring accuracy based on image data obtained by picking up animage, with use of the external CCD camera, of the caster anglemeasuring object line, comprising: original caster agile datacalculating means for calculating original caster angle data θ CAS basedon the image data when the caster angle formed between the measuringobject line and a predetermined reference line changes continuously ineither direction of increasing or decreasing; comparing means forcomparing original caster angle data θCAS(n−1) measured in a previousmeasurement timing with original caster angle data θCAS(n) measured in acurrent measurement timing; and effective data output means foroutputting the original caster angle data θ CAS(n) of the currentmeasurement as the effective caster angle data θ ECAS when thecomparison results in: θ CAS(n−1)≠θ CAS(n); and data comparing means forcomparing the current original caster angle data θ CAS(n) with measureddata of a different dimension at substantially the same time as themeasurement of the current original caster angle data θ CAS(n).
 12. Acaster angle measuring method for calculating an effective caster angleθ ECAS having a desired measuring accuracy based on image data obtainedby picking up an image, with use of an external CCD camera of a casterangle measuring object line provided on a wheel alignment measuringtarget plate attached to a vehicle, comprising the steps of: calculatingan original caster angle θ CAS by quantizing the caster angle formedbetween the measuring object line and a predetermined reference linebased on the image data; and judging the original caster angle θ CAS touse as the effective caster angle θ ECAS when the original caster angleθ CAS changes its value.
 13. The caster angle measuring method accordingto claim 12, wherein said original caster angle calculating stepcomprises the steps of: extracting the measuring object line based onthe image data; and calculating the inclination of the measuring objectline extracted by applying the method of least squares.
 14. A casterangle measuring method for calculating an effective caster angle θ ECAShaving a desired measuring accuracy based on image data obtained bypicking up an image, with use of an external CCD camera of a casterangle measuring object line provided on a wheel alignment measuringtarget plate attached to a vehicle, comprising the steps of: calculatingan original caster angle θ CAS based on the image data when the casterangle formed between the measuring object line and a predeterminedreference line changes continuously in either direction of increasing ordecreasing; comparing an original caster angle θ CAS(n−1) measured in aprevious measurement timing with an original caster angle θ CAS(n)measured in a current measurement timing; and judging the currentoriginal caster angle θ CAS(n) to use as an effective caster angle θECAS when the comparison results in: θ CAS(n−1)≠θ CAS(n).
 15. The casterangle measuring method according to claim 14, wherein said originalcaster angle calculating step comprises the steps of: extracting themeasuring object line based on the image data; and calculating theinclination of the measuring object line extracted by applying themethod of least squares.
 16. A wheel alignment measuring methodcomprising the steps of: picking up an image of a caster angle measuringobject line provided on a wheel alignment measuring target plateattached to a vehicle; calculating an original caster angle θ CAS byquantizing the caster angle formed between the picked-up measuringobject line and a predetermined reference line; judging the originalcaster angle θ CAS to use as the effective caster angle θ ECAS when thecaster angle θ CAS changes its value; and comparing the effective casterangle θ ECAS with measured data of a different dimension atsubstantially the same time when there is said change in the originalcaster angle θ CAS.
 17. A wheel alignment measuring method comprisingthe steps of: picking up an image of a caster angle measuring objectline provided on a wheel alignment measuring target plate attached to avehicle; calculating an original caster angle θ CAS when the casterangle formed between the picked-up measuring object line and apredetermined reference line changes continuously in either direction ofincreasing or decreasing; comparing an original caster angle θ CAS(n−1)measured in a previous measurement timing with an original caster angleθ CAS(n) measured in a current measurement timing; judging the currentoriginal caster angle θ CAS(n) to use as an effective caster angle θECAS when the comparison results in: θ CAS(n−1)≠θ CAS(n); and comparingthe current original caster angle θ CAS(n) with measured data of adifferent dimension at substantially the same time as a timing of themeasurement of the current original caster angle θCAS(n).
 18. A wheelalignment measuring device for measuring wheel alignment comprising: ameasuring plate configured to be attached to a vehicle wheel with itsorigin of coordinate being coincide with the center of the wheel, saidmeasuring plate comprising: a first reference mark having its origin ofcoordinate at a predetermined position; a plurality of second referencemarks having their origins of coordinates at intersections, except theposition of the first reference mark, of first virtual parallel linesprovided hypothetically on a measuring surface and second virtualparallel lines provided hypothetically on the measuring surface at rightangles to the first virtual lines; and a plurality of correction linesbeing provided on the measuring surface at regular intervals and inparallel with either the first virtual lines or the second virtuallines; first image pick-up means for outputting a first picked-up imagesignal by taking a picture of a first area including said firstreference mark and said plurality of second reference marks on saidmeasuring surface of the measuring plate; second image pick-up means foroutputting a second picked-up image signal by taking a picture of asecond area which is smaller than the first area and included in thefirst area, said second image pick-up means having an optical axispositionally related beforehand with an optical axis of said first imagepick-up means; selecting means for selecting one of said secondreference marks within said second area as a selected second referencemark based on the second picked-up image signal; relative referenceposition calculating means for calculating coordinates of relativereference position on the basis of the position coordinates of theselected second reference mark by specifying said selected secondreference mark within said first area based on the first picked-up imagesignal; and position calculating means for calculating referenceposition coordinates of the origin of position given by a predeterminedposition within the second area based on the second picked-up imagesignal and the relative reference position coordinates.
 19. The wheelalignment measuring device according to claim 18, wherein said selectingmeans selects a second reference mark, which is at the nearest point tothe predetermined position within the second area, as said selectedsecond reference mark.
 20. The wheel alignment measuring deviceaccording to claim 19, further comprising color separation means foroutputting by receiving the first picked-up image signal and the secondpicked-up image signal, a first color separation picked-up image signalconsisting of a first red picked-up image signal, a first greenpicked-up image signal and a first blue picked-up image signal, and thata second color separation picked-up image signal consisting of a secondred picked-up image signal, a second green picked-up image signal, and asecond blue picked-up image signal, wherein said selecting meansspecifies the selected second reference mark based on the second colorseparation picked-up image signal, and said relative reference positioncalculating means calculates the relative reference position coordinatesbased on the first color separation picked-up image signal.
 21. Thewheel alignment measuring device according to claim 19, wherein saidrelative reference position calculating means further comprising: centerposition calculating means for calculating the center positioncoordinates of the selected second reference mark to use as the relativereference position coordinates based on the second color separationpicked-up image signal, and said position calculating means furthercomprising: relative position coordinate calculating means forcalculating the relative position coordinates of the predeterminedposition relative to the relative reference position coordinates; andorigin reference position coordinate calculating means for calculatingthe reference position coordinates of the origin of position by addingthe relative position coordinates to the center position coordinates ofsaid selected second reference mark.
 22. The wheel alignment measuringdevice according to claim 18, further comprising color separation meansfor outputting by receiving the first picked-up image signal and thesecond picked-up image signal, a first color separation picked-up imagesignal consisting of a first red picked-up image signal, a first greenpicked-up image signal and a first blue picked-up image signal, and thata second color separation picked-up image signal consisting of a secondred picked-up image signal, a second green picked-up image signal, and asecond blue picked-up image signal, wherein said selecting meansspecifies the selected second reference mark based on the second colorseparation picked-up image signal, and said relative reference positioncalculating means calculates the relative reference position coordinatesbased on the first color separation picked-up image signal.
 23. Thewheel alignment measuring device according to claim 18, furthercomprising: a plurality of distance sensors for measuring distances fromthe sensors to different positions on the measuring surface of saidmeasuring plate, and outputting measured signals; and distancecalculating means for calculating the distance from a middle pointbetween the sensors to the measuring surface and the camber angle basedon the measuring signals from the plurality of distance sensors.
 24. Awheel alignment measuring method for measuring wheel alignmentcomprising the steps of: providing a measuring plate configured to beattached to a vehicle wheel with its origin of coordinate being coincidewith the center of the wheel, said measuring plate comprising: a firstreference mark having its origin of coordinate at a predeterminedposition; a plurality of second reference marks having their origins ofcoordinates at intersections, except the position of the first referencemark, of first virtual parallel lines provided hypothetically on ameasuring surface and second virtual parallel lines providedhypothetically on the measuring surface at right angles to the firstvirtual lines; and a plurality of correction lines being provided on themeasuring surface at regular intervals and in parallel with either thefirst virtual lines or the second virtual lines; picking up an image ofa first area containing the first reference mark and the plurality ofsecond reference marks on the measuring surface of said measuring plate;picking up an image of a second area having smaller area than that ofthe first area and included in the first area; selecting any one of thesecond reference marks within the second area to use as a selectedsecond reference mark; specifying said selected second reference markwithin the first area and calculating position coordinates of saidselected second reference mark to use as relative reference positioncoordinates; and calculating reference position coordinates of theorigin of position which are position coordinates on the basis of theorigin of a predetermined position in the second area, based on therelative reference position coordinates.
 25. The wheel alignmentmeasuring method according to claim 24, wherein said selecting stepselects a second reference mark, which is at the nearest point to thepredetermined position among the second reference marks within thesecond area, as the selected second reference mark.
 26. The wheelalignment measuring method according to claim 24 further comprising thestep of: separating colors of the images picked up by said first imagepick-up step and said second image pick-up step so as to generate afirst color separated picked-up image and a second color separatedpicked-up image, wherein the specified second reference mark isspecified by said selecting step based on the second color separatedpicked-up image, and the relative reference position coordinates arecalculated by said relative reference position calculating step based onthe first color separated picked-up image.
 27. The wheel alignmentmeasuring method according to claim 24, wherein said relative referenceposition calculating step further includes a center position calculatingstep for calculating coordinates of the center position of said selectedsecond reference mark based on the second color separated picked-upimage, and said position calculating step further includes the steps of:calculating the relative position coordinates of the predeterminedposition in reference to the relative reference position coordinates;and calculating reference position coordinates of the position of originby adding the relative position coordinates to the coordinates of thecenter of the selected second reference mark.
 28. The wheel alignmentmeasuring method according to claim 24, further comprising the steps of:measuring the distances from sensors to different positions on themeasuring surface of the measuring plate; and calculating the distancefrom a middle point between the sensors to the measuring surface and thecamber angle based on the distances measured in said step of distancemeasuring.
 29. A measuring plate having a measuring surface providedwith a plurality of concentric circles having a predetermined positionas their common point of origin and grid scale lines thereon, and beingattachable to a wheel of a vehicle to be measured in such that point oforigin coincide with the center of the rotational axis of the wheel. 30.The measuring plate according to claim 29, wherein the scale linesinclude first parallel scale lines and second parallel scale lines whichare perpendicular to the first parallel scale lines, wherein theconcentric circles and the first and second parallel scale lines aredifferent colors from each other.
 31. The measuring plate according toclaim 30, wherein the concentric circles, the first parallel scale linesand the second parallel scale lines are colored differently with use ofred, green and blue colors.
 32. A wheel alignment measuring method formeasuring wheel alignment using said measuring plate of claim 30,comprising the steps of: generating picked-up image data by picking upan image of the measuring surface, said image including at least a partof one concentric circle out of said plurality of concentric circles andat least a part of the scale lines; outputting color separated picked-upimage data by implementing color separating operation to the picked-upimage data; discriminating which concentric circle is included in theimage picked up in said image pick-up step by judging from the colorseparated picked-up image data and a curvature of the concentric circlein the picked-up image; specifying the scale lines included in thepicked-up image based on the result of judgment of said judging step andthe color separated picked-up image data; and calculating the positionon said measuring plate which corresponds to a measuring object positionbased on the positional relationship between the specified scale linesand the measuring object position in the image picked up in said imagepick-up step.
 33. The wheel alignment measuring method according toclaim 32, further comprising the steps of: calculating a spin angle bymeasuring the inclination of the scale lines in the picked-up image withrespect to a predetermined reference position.
 34. A wheel alignmentmeasuring device for measuring wheel alignment using said measuringplate of claim 29, comprising: image pick-up means for picking up animage of the measuring surface, said image including at least a part ofone concentric circle out of said plurality of concentric circles and atleast a part of the scale lines; judging means for discriminating whichconcentric circle is included in the image picked up by said imagepick-up means by judging from a curvature of the concentric circle inthe picked-up image; scale line specifying means for specifying thescale lines included in the picked-up image based on the result ofjudgment of said judging means; and operation means for calculating theposition on said measuring plate which corresponds to a measuring objectposition based on the positional relationship between the specifiedscale lines and the measuring object position in the image picked up bysaid image pick-up means.
 35. The wheel alignment measuring deviceaccording to claim 34, wherein said judging means comprises: storingmeans for storing every curvature of the plurality of the concentriccircles in advance; concentric circle extracting means for extractingthe concentric circle contained in the picked-up image based on anoutput signal of said image pick-up means; curvature calculating meansfor calculating the curvature of the extracted concentric circle; andconcentric circle specifying means for specifying the concentric circleby comparing the curvature obtained by said curvature calculating meanswith the curvatures stored in said storing means.
 36. The wheelalignment measuring device according to claim 34, wherein said judgingmeans comprises: storing means for storing every curvature of theplurality of the concentric circles in advance; concentric circleextracting means for extracting the concentric circle included in thepicked-up image based on the color separated picked-up image data;curvature calculating means for calculating the curvature of theextracted concentric circle; and concentric circle specifying means forspecifying the concentric circle by comparing the curvature obtained bysaid curvature calculating means with the curvatures stored in saidstoring means.
 37. The wheel alignment measuring device according toclaim 34, further comprising: spin angle calculating means forcalculating a spin angle by measuring an angle of inclination of thescale lines in the picked-up image with respect to a predeterminedreference position.
 38. The wheel alignment measuring device formeasuring wheel alignment using said measuring plate of claim 29,comprising: image pick-up means for outputting picked-up image data bypicking up an image of the measuring surface, said image including atleast a part of one concentric circle out of said plurality ofconcentric circles and at least a part of the scale lines;color-separation means for outputting color separated picked-up imagedata by implementing color separating operation to the picked-up imagedata; judging means for discriminating which concentric circle isincluded in the image picked up by said image pick-up means by judgingfrom the color separated picked-up image data and a curvature of theconcentric circle in the picked-up image; scale line specifying meansfor specifying the scale lines included in the picked-up image based onthe result of judgment of said judging means and the color separatedpicked-up image data; and operation means for calculating the positionon said measuring plate which corresponds to a measuring object positionbased on the positional relationship between the specified scale linesand the measuring object position in the image picked up by said imagepick-up means.
 39. A wheel alignment measuring method for measuringwheel alignment using said measuring plate of claim 29, comprising thesteps of: picking up an image of the measuring surface, said imageincluding at least a part of one concentric circle out of said pluralityof concentric circles and at least a part of the scale lines;discriminating which concentric circle is included in the picked-upimage by judging from a curvature of the concentric circle included inthe picked-up image; specifying the scale lines included in thepicked-up image based on the result of judgment of said judging step;and calculating the position on the measuring plate which corresponds toa measuring object position based on the positional relationship betweenthe specified scale lines and the measuring object position in thepicked-up image.
 40. The wheel alignment measuring method according toclaim 39, wherein said judging means comprises the steps of: extractingsaid concentric circle included in the picked-up image based on thepicked-up image data; calculating a curvature of the extractedconcentric circle; and specifying the concentric circle having thecalculated curvature by comparing the calculated curvature obtained insaid step of calculating curvature with the curvatures stored inadvance.